minor #18869 Update page_creation.rst (aliber4079)

This PR was merged into the 6.3 branch.

Discussion
----------

Update page_creation.rst

making it friendlier to newbies

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/releases for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `6.x` for features of unreleased versions).

-->

Commits
-------

2f1fc2d Update page_creation.rst

Author: javiereguiluz

page_creation.rst

@@ -38,6 +38,7 @@ Suppose you want to create a page - ``/lucky/number`` - that generates a lucky (
 random) number and prints it. To do that, create a "Controller" class and a
 "controller" method inside of it::
 
+    <?php
     // src/Controller/LuckyController.php
     namespace App\Controller;