Add link to Text2dBundle in TextBundle docs. (#9900)

# Objective

Some beginners spend time trying to manually set the position of a
`TextBundle`, without realizing that `Text2dBundle` exists.

## Solution

Mention `Text2dBundle` in the documentation of `TextBundle`.

---------

Co-authored-by: Rob Parrett <robparrett@gmail.com>

crates/bevy_ui/src/node_bundles.rs

@@ -159,6 +159,9 @@ pub struct AtlasImageBundle {
 
 #[cfg(feature = "bevy_text")]
 /// A UI node that is text
+///
+/// The positioning of this node is controlled by the UI layout system. If you need manual control,
+/// use [`Text2dBundle`](bevy_text::Text2dBundle).
 #[derive(Bundle, Debug)]
 pub struct TextBundle {
     /// Describes the logical size of the node