Add missing comment

Author: janek109

forms.rst

@@ -659,6 +659,7 @@ the choice is ultimately up to you.
     good idea to explicitly specify the ``data_class`` option by adding the
     following to your form type class::
 
+        // src/AppBundle/Form/TaskType.php
         use AppBundle\Entity\Task;
         use Symfony\Component\OptionsResolver\OptionsResolver;