README: Add link to google group.
README: Add link to google group.

jonnylamb/weston,giucam/weston,mchalupa/weston,Gnurou/weston,eyolfson/wayland,eyolfson/wayland,tulcod/wayland,sir-murray/weston,mchalupa/wayland,bitfactor/wayland,kwm81/weston,mchalupa/wayland,sir-murray/wayland,abooij/wayland,sir-murray/wayland,kwm81/weston,Tarnyko/weston-xdg_surface_present,Gnurou/weston,eyolfson/weston,jonnylamb/weston,mchalupa/weston,eyolfson/wayland,Fantu/compositor-spice,tulcod/wayland,sir-murray/wayland,Fantu/compositor-spice,Fantu/compositor-spice,xorgy/weston,krezovic/weston,udoprog/weston,mchalupa/wayland,abooij/wayland,tulcod/wayland,Tarnyko/weston-xdg_surface_present,krezovic/weston,bitfactor/wayland,eyolfson/weston,xorgy/weston,udoprog/weston,sir-murray/weston,giucam/weston,abooij/wayland,bitfactor/wayland