xdg-shell: Document responsibilities regarding ping events
xdg-shell: Document responsibilities regarding ping events

Document that a compositor is free to ping in any way it wants, but a
client must always respond to any xdg_shell object it created.

Signed-off-by: Jonas Ådahl <67dcd8a17e758192e0cbb577ce1d62cc7da6cf49@gmail.com>

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