Added tip for Entity Listeners

Author: Slava Fomin

cookbook/doctrine/event_listeners_subscribers.rst

@@ -154,6 +154,12 @@ specific type of entity (e.g. a ``Product`` entity but not a ``BlogPost``
 entity), you should check for the entity's class type in your method
 (as shown above).
 
+.. tip::
+
+    Starting from version 2.4 Doctrine has a feature called `Entity Listeners`_
+    which is a lifecycle listener class used for an entity. You can read about
+    it in Doctrine documentation.
+
 Creating the Subscriber Class
 -----------------------------
 
@@ -211,3 +217,4 @@ interface and have an event method for each event it subscribes to::
 For a full reference, see chapter `The Event System`_ in the Doctrine documentation.
 
 .. _`The Event System`: http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/events.html
+.. _`Entity Listeners`: http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/events.html#entity-listeners