Clarify Texture Atlas rework migration guide

content/learn/migration-guides/0.12-to-0.13.md

@@ -878,6 +878,10 @@ Renamed `PbrInput::occlusion` to `diffuse_occlusion`, and added `specular_occlus
     <div class="migration-guide-area-tag">Rendering</div>
 </div>
 
+The `TextureAtlas` asset that previously contained both the atlas layout and image handle has been renamed to `TextureAtlasLayout` that only contains the layout now. A separate `Handle<Image>`gotten through either `SpriteSheetBundle::texture` or `AtlasImageBundle::image` replaces the prior image handle functionality of `TextureAtlasLayout`.
+
+`TextureAtlasSprite` was removed and replaced by a new component, `TextureAtlas`, which now holds the atlas index and is a direct component of `SpriteSheetBundle` replacing the `Handle<TextureAtlasLayout>` from before. The `Sprite` component can be used for `flip_x`, `flip_y`, `custom_size`, `anchor`, and `color` and replaces `TextureAtlasSprite` in `SpriteSheetBundle`.
+
 - Sprites
 
 ```diff
@@ -894,12 +898,14 @@ fn my_system(
     commands.spawn(SpriteSheetBundle {
 -      sprite: TextureAtlasSprite::new(0),
 -      texture_atlas: atlas_handle,
+       // the new sprite initialization is covered by the `..default()` expression; however, it is added to showcase migration
++      sprite: Sprite::default()
 +      atlas: TextureAtlas {
 +         layout: layout_handle,
 +         index: 0
 +      },
 +      texture: texture_handle,
-       ..Default::default()
+       ..default()
      });
 }
 ```
@@ -933,7 +939,7 @@ fn my_system(
 +           flip_x: false,
 +           flip_y: false,
 +       },
-       ..Default::default()
+       ..default()
      });
 }
 ```