Document changing menus of raspi-config

The options on `raspi-config` will now change depending on which Raspberry Pi hardware it's running on post-Bookworm. This needs documenting. The decision I've made for #2955 is to document the Pi 4 case only right now with a `NOTE` to say that there will be changes depending on what hardware you're on.

We probably need to document this properly at some point, but I don't see it as urgent.