Docs reflect that RemovalDetection also yields despawned entities

[porkbrain]

Objective

I want to keep track of despawned entities.
I am aware of RemovedComponents.
However, the docs don't explicitly mention that despawned entities are also included in this event iterator.
I searched through the bevy tests to find removal_tracking in crates/bevy_ecs/src/system/mod.rs that confirmed the behavior:

            ...
            assert_eq!(
                removed_i32.read().collect::<Vec<_>>(),
                &[despawned.0],
                "despawning causes the correct entity to show up in the 'RemovedComponent' system parameter."
            );
            ...

Solution

• Explicitly mention this behavior in docs.

[shanecelis]

I wasn't sure about the despawn behavior, so I double checked it, and it's right. TIL. Approved.