Added a more useful message for users that don't have PHP 5.4

and try to execute the server:run command

Author: javiereguiluz

quick_tour/the_big_picture.rst

@@ -54,18 +54,19 @@ to run Symfony:
 
     $ php app/console server:run
 
+If you get the error `There are no commands defined in the "server" namespace.`,
+then you are probably using PHP 5.3. That's ok! But the built-in web server is
+available for PHP 5.4.0 or higher. If you have an older version of PHP or if you
+prefer a traditional web server such as Apache or Nginx, read the
+:doc:`/cookbook/configuration/web_server_configuration` article.
+
 Open your browser and access to the ``http://localhost:8000`` URL to
 see the Welcome page of Symfony2:
 
 .. image:: /images/quick_tour/welcome.png
    :align: center
    :alt:   Symfony2 Welcome Page
 
-The built-in web server is available for PHP 5.4.0 or higher. If you have an
-older version of PHP or if you prefer a traditional web server such as Apache
-or Nginx, read the :doc:`/cookbook/configuration/web_server_configuration`
-article.
-
 Understanding the Fundamentals
 ------------------------------