Add a link to the notifications page from the Object class page (#5465)

Co-authored-by: Hugo Locurcio <hugo.locurcio@hugo.pro>
(cherry picked from commit a4746a2366)

development/cpp/object_class.rst

@@ -237,6 +237,13 @@ Adding signals to a class is done in ``_bind_methods``, using the
 
     ADD_SIGNAL(MethodInfo("been_killed"))
 
+Notifications
+-------------
+
+All objects in Godot have a :ref:`_notification <class_Object_method__notification>`
+method that allows it to respond to engine level callbacks that may relate to it.
+More information can be found on the :ref:`doc_godot_notifications` page.
+
 References
 ----------