completion: Complete gsettings describe
completion: Complete gsettings describe

Commit 8fd72838 added a 'describe' command to the gsettings tool,
but didn't implement completions for it.

https://bugzilla.gnome.org/show_bug.cgi?id=772297

johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib