chore: notes for crosshair implementation

src/ui/crosshair.rs

@@ -5,6 +5,29 @@ use bevy::prelude::*;
 // For now, we'll just draw a crosshair in the center of the screen.
 // This causes a lot of warnings without a camera!
 
+/*
+In bevy 0.15.x, you can automatically insert components based on other components using required components
+https://docs.rs/bevy/latest/bevy/ecs/component/trait.Component.html#required-components
+
+For removal, I would implement it using component hooks
+https://docs.rs/bevy/latest/bevy/ecs/component/struct.ComponentHooks.html
+
+An example where adding or removing A adds or removes B:
+```rust
+#[derive(Component)]
+pub struct B;
+
+#[derive(Component)]
+#[require(B)]
+#[component(on_remove = remove_B)]
+pub struct A;
+
+fn remove_B(world : DefferedWorld, entity : Entity, _id : ComponentId) {
+  world.commands().entity(entity).remove::<B>();
+}
+```
+*/
+
 pub struct CrosshairPlugin;
 
 impl Plugin for CrosshairPlugin