@aferrandini, thank you for your contribution! But you did the indentation wrong, you should indent everything inside a block with 4 spaces, code blocks included.

So this should be:

````rst
.. tip::

    If you are using the Symfony Standard Edition, configure the parameters at ``parameters.yml``:

    .. code-block:: yaml

        # app/config/parameters.yml
        parameters:
            ...
            mailer_transport: gmail
            mailer_host:        ~
            mailer_user:        your_gmail_username
            mailer_password: your_gmail_password

Please notice that I also added the word `the` before `Symfony Standard Edition`, that sounds better.