Fixup docs

Author: DJMcNab

crates/bevy_render/src/extract_param.rs

@@ -36,6 +36,10 @@ impl<P: SystemParam> FromWorld for MainWorldState<P> {
 /// ## Examples
 ///
 /// ```rust
+/// use bevy_ecs::prelude::*;
+/// use bevy_render::Extract;
+/// # #[derive(Component)]
+/// # struct Cloud;
 /// fn extract_clouds(mut commands: Commands, mut clouds: Extract<Query<Entity, With<Cloud>>>) {
 ///     for cloud in clouds.value().iter() {
 ///         commands.get_or_spawn(cloud).insert(Cloud);