Update keyboard.rs docs in bevy_input (#4517)

# Objective

- Part of the splitting process of #3692.

## Solution

- Document `keyboard.rs` inside of `bevy_input`.

Co-authored-by: KDecay <KDecayMusic@protonmail.com>

crates/bevy_input/src/keyboard.rs

@@ -1,16 +1,31 @@
 use crate::{ButtonState, Input};
-use bevy_ecs::event::EventReader;
+use bevy_ecs::{event::EventReader, system::ResMut};
-use bevy_ecs::system::ResMut;
 
-/// A key input event from a keyboard device
+/// A keyboard input event.
+///
+/// This event is the translated version of the `WindowEvent::KeyboardInput` from the `winit` crate.
+/// It is available to the end user and can be used for game logic.
+///
+/// ## Usage
+///
+/// The event is consumed inside of the [`keyboard_input_system`](crate::keyboard::keyboard_input_system)
+/// to update the [`Input<KeyCode>`](crate::Input<KeyCode>) resource.
 #[derive(Debug, Clone)]
 pub struct KeyboardInput {
+    /// The scan code of the key.
     pub scan_code: u32,
+    /// The key code of the key.
     pub key_code: Option<KeyCode>,
+    /// The press state of the key.
     pub state: ButtonState,
 }
 
-/// Updates the `Input<KeyCode>` resource with the latest `KeyboardInput` events
+/// Updates the [`Input<KeyCode>`] resource with the latest [`KeyboardInput`] events.
+///
+/// ## Differences
+///
+/// The main difference between the [`KeyboardInput`] event and the [`Input<KeyCode>`] resource is that
+/// the latter has convenient functions like [`Input::pressed`], [`Input::just_pressed`] and [`Input::just_released`].
 pub fn keyboard_input_system(
     mut keyboard_input: ResMut<Input<KeyCode>>,
     mut keyboard_input_events: EventReader<KeyboardInput>,
@@ -31,206 +46,364 @@ pub fn keyboard_input_system(
     }
 }
 
-/// The key code of a keyboard input.
+/// The key code of a [`KeyboardInput`](crate::keyboard::KeyboardInput).
+///
+/// ## Usage
+///
+/// It is used as the generic `T` value of an [`Input`](crate::Input) to create a `Res<Input<KeyCode>>`.
+/// The resource stores the data of the buttons of a keyboard and can be accessed inside of a system.
+///
+/// ## Updating
+///
+/// The resource is updated inside of the [`keyboard_input_system`](crate::keyboard::keyboard_input_system).
 #[derive(Debug, Hash, Ord, PartialOrd, PartialEq, Eq, Clone, Copy)]
 #[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[repr(u32)]
 pub enum KeyCode {
-    /// The '1' key over the letters.
+    /// The `1` key over the letters.
     Key1,
-    /// The '2' key over the letters.
+    /// The `2` key over the letters.
     Key2,
-    /// The '3' key over the letters.
+    /// The `3` key over the letters.
     Key3,
-    /// The '4' key over the letters.
+    /// The `4` key over the letters.
     Key4,
-    /// The '5' key over the letters.
+    /// The `5` key over the letters.
     Key5,
-    /// The '6' key over the letters.
+    /// The `6` key over the letters.
     Key6,
-    /// The '7' key over the letters.
+    /// The `7` key over the letters.
     Key7,
-    /// The '8' key over the letters.
+    /// The `8` key over the letters.
     Key8,
-    /// The '9' key over the letters.
+    /// The `9` key over the letters.
     Key9,
-    /// The '0' key over the 'O' and 'P' keys.
+    /// The `0` key over the letters.
     Key0,
 
+    /// The `A` key.
     A,
+    /// The `B` key.
     B,
+    /// The `C` key.
     C,
+    /// The `D` key.
     D,
+    /// The `E` key.
     E,
+    /// The `F` key.
     F,
+    /// The `G` key.
     G,
+    /// The `H` key.
     H,
+    /// The `I` key.
     I,
+    /// The `J` key.
     J,
+    /// The `K` key.
     K,
+    /// The `L` key.
     L,
+    /// The `M` key.
     M,
+    /// The `N` key.
     N,
+    /// The `O` key.
     O,
+    /// The `P` key.
     P,
+    /// The `Q` key.
     Q,
+    /// The `R` key.
     R,
+    /// The `S` key.
     S,
+    /// The `T` key.
     T,
+    /// The `U` key.
     U,
+    /// The `V` key.
     V,
+    /// The `W` key.
     W,
+    /// The `X` key.
     X,
+    /// The `Y` key.
     Y,
+    /// The `Z` key.
     Z,
 
-    /// The Escape key, next to F1.
+    /// The `Escape` / `ESC` key, next to the `F1` key.
     Escape,
 
+    /// The `F1` key.
     F1,
+    /// The `F2` key.
     F2,
+    /// The `F3` key.
     F3,
+    /// The `F4` key.
     F4,
+    /// The `F5` key.
     F5,
+    /// The `F6` key.
     F6,
+    /// The `F7` key.
     F7,
+    /// The `F8` key.
     F8,
+    /// The `F9` key.
     F9,
+    /// The `F10` key.
     F10,
+    /// The `F11` key.
     F11,
+    /// The `F12` key.
     F12,
+    /// The `F13` key.
     F13,
+    /// The `F14` key.
     F14,
+    /// The `F15` key.
     F15,
+    /// The `F16` key.
     F16,
+    /// The `F17` key.
     F17,
+    /// The `F18` key.
     F18,
+    /// The `F19` key.
     F19,
+    /// The `F20` key.
     F20,
+    /// The `F21` key.
     F21,
+    /// The `F22` key.
     F22,
+    /// The `F23` key.
     F23,
+    /// The `F24` key.
     F24,
 
-    /// Print Screen/SysRq.
+    /// The `Snapshot` / `Print Screen` key.
     Snapshot,
-    /// Scroll Lock.
+    /// The `Scroll` / `Scroll Lock` key.
     Scroll,
-    /// Pause/Break key, next to Scroll lock.
+    /// The `Pause` / `Break` key, next to the `Scroll` key.
     Pause,
 
-    /// `Insert`, next to Backspace.
+    /// The `Insert` key, next to the `Backspace` key.
     Insert,
+    /// The `Home` key.
     Home,
+    /// The `Delete` key.
     Delete,
+    /// The `End` key.
     End,
+    /// The `PageDown` key.
     PageDown,
+    /// The `PageUp` key.
     PageUp,
 
+    /// The `Left` / `Left Arrow` key.
     Left,
+    /// The `Up` / `Up Arrow` key.
     Up,
+    /// The `Right` / `Right Arrow` key.
     Right,
+    /// The `Down` / `Down Arrow` key.
     Down,
 
-    /// The Backspace key, right over Enter.
+    /// The `Back` / `Backspace` key.
     Back,
-    /// The Enter key.
+    /// The `Return` / `Enter` key.
     Return,
-    /// The space bar.
+    /// The `Space` / `Spacebar` / ` ` key.
     Space,
 
-    /// The "Compose" key on Linux.
+    /// The `Compose` key on Linux.
     Compose,
-
+    /// The `Caret` / `^` key.
     Caret,
 
+    /// The `Numlock` key.
     Numlock,
+    /// The `Numpad0` / `0` key.
     Numpad0,
+    /// The `Numpad1` / `1` key.
     Numpad1,
+    /// The `Numpad2` / `2` key.
     Numpad2,
+    /// The `Numpad3` / `3` key.
     Numpad3,
+    /// The `Numpad4` / `4` key.
     Numpad4,
+    /// The `Numpad5` / `5` key.
     Numpad5,
+    /// The `Numpad6` / `6` key.
     Numpad6,
+    /// The `Numpad7` / `7` key.
     Numpad7,
+    /// The `Numpad8` / `8` key.
     Numpad8,
+    /// The `Numpad9` / `9` key.
     Numpad9,
 
+    /// The `AbntC1` key.
     AbntC1,
+    /// The `AbntC2` key.
     AbntC2,
+
+    /// The `NumpadAdd` / `+` key.
     NumpadAdd,
+    /// The `Apostrophe` / `'` key.
     Apostrophe,
+    /// The `Apps` key.
     Apps,
+    /// The `Asterik` / `*` key.
     Asterisk,
+    /// The `Plus` / `+` key.
     Plus,
+    /// The `At` / `@` key.
     At,
+    /// The `Ax` key.
     Ax,
+    /// The `Backslash` / `\` key.
     Backslash,
+    /// The `Calculator` key.
     Calculator,
+    /// The `Capital` key.
     Capital,
+    /// The `Colon` / `:` key.
     Colon,
+    /// The `Comma` / `,` key.
     Comma,
+    /// The `Convert` key.
     Convert,
+    /// The `NumpadDecimal` / `.` key.
     NumpadDecimal,
+    /// The `NumpadDivide` / `/` key.
     NumpadDivide,
+    /// The `Equals` / `=` key.
     Equals,
+    /// The `Grave` / `Backtick` / `` ` `` key.
     Grave,
+    /// The `Kana` key.
     Kana,
+    /// The `Kanji` key.
     Kanji,
-    /// The left alt key. Maps to left option on Mac.
+
+    /// The `LAlt` / `Left Alt` key. Maps to `Left Option` on Mac.
     LAlt,
+    /// The `LBracket` / `Left Bracket` key.
     LBracket,
+    /// The `LControl` / `Left Control` key.
     LControl,
+    /// The `LShift` / `Left Shift` key.
     LShift,
-    /// The left Windows key. Maps to left Command on Mac.
+    /// The `LWin` / `Left Windows` key. Maps to `Left Command` on Mac.
     LWin,
+
+    /// The `Mail` key.
     Mail,
+    /// The `MediaSelect` key.
     MediaSelect,
+    /// The `MediaStop` key.
     MediaStop,
+    /// The `Minus` / `-` key.
     Minus,
+    /// The `NumpadMultiply` / `*` key.
     NumpadMultiply,
+    /// The `Mute` key.
     Mute,
+    /// The `MyComputer` key.
     MyComputer,
-    NavigateForward,  // also called "Prior"
+    /// The `NavigateForward` / `Prior` key.
-    NavigateBackward, // also called "Next"
+    NavigateForward,
+    /// The `NavigateBackward` / `Next` key.
+    NavigateBackward,
+    /// The `NextTrack` key.
     NextTrack,
+    /// The `NoConvert` key.
     NoConvert,
+    /// The `NumpadComma` / `,` key.
     NumpadComma,
+    /// The `NumpadEnter` key.
     NumpadEnter,
+    /// The `NumpadEquals` / `=` key.
     NumpadEquals,
+    /// The `Oem102` key.
     Oem102,
+    /// The `Period` / `.` key.
     Period,
+    /// The `PlayPause` key.
     PlayPause,
+    /// The `Power` key.
     Power,
+    /// The `PrevTrack` key.
     PrevTrack,
-    /// The right alt key. Maps to right option on Mac.
+
+    /// The `RAlt` / `Right Alt` key. Maps to `Right Option` on Mac.
     RAlt,
+    /// The `RBracket` / `Right Bracket` key.
     RBracket,
+    /// The `RControl` / `Right Control` key.
     RControl,
+    /// The `RShift` / `Right Shift` key.
     RShift,
-    /// The right Windows key. Maps to right Command on Mac.
+    /// The `RWin` / `Right Windows` key. Maps to `Right Command` on Mac.
     RWin,
+
+    /// The `Semicolon` / `;` key.
     Semicolon,
+    /// The `Slash` / `/` key.
     Slash,
+    /// The `Sleep` key.
     Sleep,
+    /// The `Stop` key.
     Stop,
+    /// The `NumpadSubtract` / `-` key.
     NumpadSubtract,
+    /// The `Sysrq` key.
     Sysrq,
+    /// The `Tab` / `   ` key.
     Tab,
+    /// The `Underline` / `_` key.
     Underline,
+    /// The `Unlabeled` key.
     Unlabeled,
+
+    /// The `VolumeDown` key.
     VolumeDown,
+    /// The `VolumeUp` key.
     VolumeUp,
+
+    /// The `Wake` key.
     Wake,
+
+    /// The `WebBack` key.
     WebBack,
+    /// The `WebFavorites` key.
     WebFavorites,
+    /// The `WebForward` key.
     WebForward,
+    /// The `WebHome` key.
     WebHome,
+    /// The `WebRefresh` key.
     WebRefresh,
+    /// The `WebSearch` key.
     WebSearch,
+    /// The `WebStop` key.
     WebStop,
+
+    /// The `Yen` key.
     Yen,
+
+    /// The `Copy` key.
     Copy,
+    /// The `Paste` key.
     Paste,
+    /// The `Cut` key.
     Cut,
 }