document which lifetime is needed for systemparam derive

crates/bevy_ecs/src/system/system_param.rs

@@ -36,6 +36,35 @@ use std::{
 /// Derived `SystemParam` structs may have two lifetimes: `'w` for data stored in the [`World`],
 /// and `'s` for data stored in the parameter's state.
 ///
+/// The following list shows the most common SystemParams and which lifetime they require
+///
+/// ```
+/// # use bevy_ecs::prelude::*;
+/// # #[derive(Resource)]
+/// # struct SomeResource;
+/// # #[derive(Event)]
+/// # struct SomeEvent;
+/// # #[derive(Resource)]
+/// # struct SomeOtherResource;
+/// # use bevy_ecs::system::SystemParam;
+/// # #[derive(SystemParam)]
+/// # struct ParamsExample<'w, 's> {
+/// #    query:
+/// Query<'w, 's, Entity>,
+/// #    res:
+/// Res<'w, SomeResource>,
+/// #    res_mut:
+/// ResMut<'w, SomeOtherResource>,
+/// #    local:
+/// Local<'s, u8>,
+/// #    commands:
+/// Commands<'w, 's>,
+/// #    eventreader:
+/// EventReader<'w, 's, SomeEvent>,
+/// #    eventwriter:
+/// EventWriter<'w, SomeEvent>
+/// # }
+///```
 /// ## `PhantomData`
 ///
 /// [`PhantomData`] is a special type of `SystemParam` that does nothing.