Document making props reactive with readonlysignal in the reference

The inline documentation has a section on [making props reactive](https://docs.rs/dioxus-core-macro/latest/dioxus_core_macro/attr.component.html#reactive-props), but the reference on the docsite does not. We should move that section into the reference or re-organize the [component reference](https://dioxuslabs.com/learn/0.6/reference/component_props#) to point to the docsite for details more prominently