`World::init_component` docs do not explain that components are generally automatically initialized

[alice-i-cecile]

How can Bevy's documentation be improved?

init_component is used to register components for use. However, when using systems, components are automatically registered when the system is initialized.

This was spotted when reviewing #16434, which suggests that you call this method if World::try_query fails.

[VitalyAnkh]

init_component has been renamed to register_component.