Add link to notification docs in SceneTree docs

doc/classes/SceneTree.xml

@@ -156,7 +156,7 @@
 			<param index="0" name="group" type="StringName" />
 			<param index="1" name="notification" type="int" />
 			<description>
-				Calls [method Object.notification] with the given [param notification] to all nodes inside this tree added to the [param group]. See also [method call_group] and [method set_group].
+				Calls [method Object.notification] with the given [param notification] to all nodes inside this tree added to the [param group]. See also [url=$DOCS_URL/tutorials/best_practices/godot_notifications.html]Godot notifications[/url] and [method call_group] and [method set_group].
 				[b]Note:[/b] This method acts immediately on all selected nodes at once, which may cause stuttering in some performance-intensive situations.
 			</description>
 		</method>