minor #9358 Missing the obvious <?php (nasaralla)

This PR was submitted for the 4.0 branch but it was merged into the 2.7 branch instead (closes #9358).

Discussion
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Missing the obvious <?php

Simple missing <?php had me wondering for an hour

Commits
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261dd81 Missing the obvious <?php

Author: javiereguiluz

page_creation.rst

@@ -39,6 +39,7 @@ random) number and prints it. To do that, create a "Controller class" and a
 "controller" method inside of it that will be executed when someone goes to
 ``/lucky/number``::
 
+    <?php
     // src/AppBundle/Controller/LuckyController.php
     namespace AppBundle\Controller;