docs: Reorder some sections
docs: Reorder some sections

Move the 'Types of Compositors' section right after the Overview,
and move the 'Client API' part after the protocol spec.

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