Added link to Babel's message extracting functionality.

.. admonition:: Using Jinja2 templates?

    :djadmin:`makemessages` doesn't understand the syntax of Jinja2 templates.

    To extract strings from a project containing Jinja2 templates, use Babel_

    instead.

    To extract strings from a project containing Jinja2 templates, use `Message

    Extracting`_ from Babel_ instead.

    Here's an example ``babel.cfg`` configuration file::

    in general, and doesn't depend on ``gettext``. For more information, read

    its documentation about `working with message catalogs`_.

    .. _Message extracting: http://babel.pocoo.org/docs/messages/#message-extraction

    .. _Babel: http://babel.pocoo.org/

    .. _working with message catalogs: http://babel.pocoo.org/docs/messages/