minor #12501 Added namespace for example controller (TheGarious)

This PR was squashed before being merged into the 4.3 branch (closes #12501).

Discussion
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Added namespace for example controller

I have a question.

Do i need added "<?php" for each example function in php in this docs ?

If yes, i create a new PR with all example with added <?php for each php example.

Thanks

Commits
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1f88d28 Added namespace for example controller

Author: javiereguiluz

page_creation.rst

@@ -217,6 +217,7 @@ Now, use the handy ``render()`` function to render a template. Pass it a ``numbe
 variable so you can use it in Twig::
 
     // src/Controller/LuckyController.php
+    namespace App\Controller;
 
     // ...
     class LuckyController extends AbstractController