protocol: Add summary description for wl_data_device_manager
protocol: Add summary description for wl_data_device_manager

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