Made the naming for commands parameter more consistent (#14851)

# Objective

Make the naming of a parameter more consistent.

## Solution

- Changing the name of a parameter.

## Testing

These changes can't be tested as they are documentation based.

---

I apologize if something is wrong here, this is my first PR to bevy.

examples/window/window_resizing.rs

@@ -27,14 +27,15 @@ struct ResolutionSettings {
 }
 
 // Spawns the camera that draws UI
-fn setup_camera(mut cmd: Commands) {
-    cmd.spawn(Camera2dBundle::default());
+fn setup_camera(mut commands: Commands) {
+    commands.spawn(Camera2dBundle::default());
 }
 
 // Spawns the UI
-fn setup_ui(mut cmd: Commands) {
+fn setup_ui(mut commands: Commands) {
     // Node that fills entire background
-    cmd.spawn(NodeBundle {
+    commands
+        .spawn(NodeBundle {
             style: Style {
                 width: Val::Percent(100.),
                 ..default()