Improved some help notes

Author: javiereguiluz

src/AppBundle/Controller/BlogController.php

@@ -98,9 +98,17 @@ public function commentNewAction(Request $request, Post $post)
             $entityManager->persist($comment);
             $entityManager->flush();
 
+            // When triggering an event, you can optionally pass some information.
+            // For simple applications, use the GenericEvent object provided by Symfony
+            // to pass some PHP variables. For more complex applications, define your
+            // own event object classes.
             // See http://symfony.com/doc/current/components/event_dispatcher/generic_event.html
             $event = new GenericEvent($comment);
 
+            // When an event is dispatched, Symfony notifies it to all the listeners
+            // and subscribers registered to it. Listeners can modify the information
+            // passed in the event and they can even modify the execution flow, so
+            // there's no guarantee that the rest of this controller will be executed.
             // See http://symfony.com/doc/current/components/event_dispatcher.html
             $this->get('event_dispatcher')->dispatch(Events::COMMENT_CREATED, $event);