protocol: Document how clients are supposed to get the xkb keycode
protocol: Document how clients are supposed to get the xkb keycode

This encodes what everyone is doing and avoids other implementers
having to guess.

eyolfson/wayland,abooij/wayland,tulcod/wayland,tulcod/wayland,bitfactor/wayland,bitfactor/wayland,mchalupa/wayland,bitfactor/wayland,sir-murray/wayland,mchalupa/wayland,tulcod/wayland,sir-murray/wayland,eyolfson/wayland,abooij/wayland,eyolfson/wayland,sir-murray/wayland,mchalupa/wayland,abooij/wayland