Document the wlr_output_layout_get function

include/wlr/types/wlr_output_layout.h

@@ -54,6 +54,10 @@ struct wlr_output_layout *wlr_output_layout_create(void);
 
 void wlr_output_layout_destroy(struct wlr_output_layout *layout);
 
+/**
+ * Get the output layout for the specified output. Returns NULL if no output
+ * matches.
+ */
 struct wlr_output_layout_output *wlr_output_layout_get(
 		struct wlr_output_layout *layout, struct wlr_output *reference);