Rewrite part of Commands rustdoc (#11141)

- Explain it is flushed in the same schedule run (was not obvious to me)
- Point to `apply_deferred` example
- Remove mentions of `System::apply_deferred` and
`Schedule::apply_deferred` which are probably too low level for the most
users

Co-authored-by: James Liu <contact@jamessliu.com>

crates/bevy_ecs/src/schedule/executor/mod.rs

@@ -93,9 +93,20 @@ impl SystemSchedule {
 }
 
 /// Instructs the executor to call [`System::apply_deferred`](crate::system::System::apply_deferred)
-/// on the systems that have run but not applied their [`Deferred`](crate::system::Deferred) system parameters (like [`Commands`](crate::prelude::Commands)) or other system buffers.
+/// on the systems that have run but not applied their [`Deferred`](crate::system::Deferred) system parameters
+/// (like [`Commands`](crate::prelude::Commands)) or other system buffers.
 ///
-/// **Notes**
+/// ## Scheduling
+///
+/// `apply_deferred` systems are scheduled *by default*
+/// - later in the same schedule run (for example, if a system with `Commands` param
+///   is scheduled in `Update`, all the changes will be visible in `PostUpdate`)
+/// - between systems with dependencies if the dependency
+///   [has deferred buffers](crate::system::System::has_deferred)
+///   (if system `bar` directly or indirectly depends on `foo`, and `foo` uses `Commands` param,
+///   changes to the world in `foo` will be visible in `bar`)
+///
+/// ## Notes
 /// - This function (currently) does nothing if it's called manually or wrapped inside a [`PipeSystem`](crate::system::PipeSystem).
 /// - Modifying a [`Schedule`](super::Schedule) may change the order buffers are applied.
 #[doc(alias = "apply_system_buffers")]

crates/bevy_ecs/src/system/commands/mod.rs

@@ -17,11 +17,7 @@ use std::marker::PhantomData;
 ///
 /// Since each command requires exclusive access to the `World`,
 /// all queued commands are automatically applied in sequence
-/// when the [`apply_deferred`] system runs.
+/// when the `apply_deferred` system runs (see [`apply_deferred`] documentation for more details).
-///
-/// The command queue of an individual system can also be manually applied
-/// by calling [`System::apply_deferred`].
-/// Similarly, the command queue of a schedule can be manually applied via [`Schedule::apply_deferred`].
 ///
 /// Each command can be used to modify the [`World`] in arbitrary ways:
 /// * spawning or despawning entities
@@ -67,9 +63,7 @@ use std::marker::PhantomData;
 /// # }
 /// ```
 ///
-/// [`System::apply_deferred`]: crate::system::System::apply_deferred
 /// [`apply_deferred`]: crate::schedule::apply_deferred
-/// [`Schedule::apply_deferred`]: crate::schedule::Schedule::apply_deferred
 #[derive(SystemParam)]
 pub struct Commands<'w, 's> {
     queue: Deferred<'s, CommandQueue>,