Fixed #22753 -- Documented ability to use a note with the {% comment %} tag.

^^^^^^^

Ignores everything between ``{% comment %}`` and ``{% endcomment %}``.

An optional note may be inserted in the first tag. For example, this is

useful when commenting out code for documenting why the code was disabled.

Sample usage::

    <p>Rendered text with {{ pub_date|date:"c" }}</p>

    {% comment %}

    {% comment "Optional note" %}

        <p>Commented out text with {{ create_date|date:"c" }}</p>

    {% endcomment %}