doc: change wording in section introduction
doc: change wording in section introduction

If we don't have descriptions of classes, the "And" is awkward.

Signed-off-by: Peter Hutterer <b9c50af7afa7642f6f854434cda9ffe54ece8b85@who-t.net>

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