adding compile call to overriding parent services section

Author: Grayson Koonce

components/dependency_injection/parentservices.rst

@@ -367,6 +367,7 @@ to the ``NewsletterManager`` class, the config would look like this:
     .. code-block:: php
 
         use Symfony\Component\DependencyInjection\Definition;
+        use Symfony\Component\DependencyInjection\DefinitionDecorator;
         use Symfony\Component\DependencyInjection\Reference;
 
         // ...
@@ -399,6 +400,8 @@ to the ``NewsletterManager`` class, the config would look like this:
             '%greeting_card_manager.class%'
         );
 
+        $container->compile();
+
 The ``GreetingCardManager`` will receive the same dependencies as before,
 but the ``NewsletterManager`` will be passed the ``my_alternative_mailer``
 instead of the ``my_mailer`` service.