Add move sprite example. (#2414)

## Objective
There is no bevy example that shows how to transform a sprite. At least as its singular purpose. This creates an example of how to use transform.translate to move a sprite up and down. The last pull request had issues that I couldn't fix so I created a new one

### Solution
I created move_sprite example.

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

Cargo.toml

@@ -119,6 +119,10 @@ path = "examples/2d/contributors.rs"
 name = "many_sprites"
 path = "examples/2d/many_sprites.rs"
 
+[[example]]
+name = "move_sprite"
+path = "examples/2d/move_sprite.rs"
+
 [[example]]
 name = "2d_rotation"
 path = "examples/2d/rotation.rs"

examples/2d/move_sprite.rs

@@ -0,0 +1,41 @@
+use bevy::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(setup)
+        .add_system(sprite_movement)
+        .run();
+}
+
+#[derive(Component)]
+enum Direction {
+    Up,
+    Down,
+}
+
+fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
+    commands
+        .spawn_bundle(SpriteBundle {
+            texture: asset_server.load("branding/icon.png"),
+            transform: Transform::from_xyz(100., 0., 0.),
+            ..Default::default()
+        })
+        .insert(Direction::Up);
+}
+
+fn sprite_movement(time: Res<Time>, mut sprite_position: Query<(&mut Direction, &mut Transform)>) {
+    for (mut logo, mut transform) in sprite_position.iter_mut() {
+        match *logo {
+            Direction::Up => transform.translation.y += 150. * time.delta_seconds(),
+            Direction::Down => transform.translation.y -= 150. * time.delta_seconds(),
+        }
+
+        if transform.translation.y > 200. {
+            *logo = Direction::Down;
+        } else if transform.translation.y < -200. {
+            *logo = Direction::Up;
+        }
+    }
+}

examples/README.md

@@ -84,6 +84,7 @@ Example | File | Description
 --- | --- | ---
 `contributors` | [`2d/contributors.rs`](./2d/contributors.rs) | Displays each contributor as a bouncy bevy-ball!
 `many_sprites` | [`2d/many_sprites.rs`](./2d/many_sprites.rs) | Displays many sprites in a grid arragement! Used for performance testing.
+`move_sprite` | [`2d/move_sprite.rs`](./2d/move_sprite.rs) | Changes the transform of a sprite.
 `mesh2d` | [`2d/mesh2d.rs`](./2d/mesh2d.rs) | Renders a 2d mesh
 `mesh2d_manual` | [`2d/mesh2d_manual.rs`](./2d/mesh2d_manual.rs) | Renders a custom mesh "manually" with "mid-level" renderer apis.
 `rect` | [`2d/rect.rs`](./2d/rect.rs) | Renders a rectangle