[1.8.x] Clarified default value for DateField to emulate auto_now_add.

    for creation of timestamps. Note that the current date is *always* used;

    it's not just a default value that you can override. So even if you

    set a value for this field when creating the object, it will be ignored.

    If you want to be able to modify this field, set ``default=timezone.now``

    (from :func:`django.utils.timezone.now`) instead of ``auto_now_add=True``.

    If you want to be able to modify this field, set the following instead of

    ``auto_now_add=True``:

    * For :class:`DateField`: ``default=date.today`` - from

      :meth:`datetime.date.today`

    * For :class:`DateTimeField`: ``default=timezone.now`` - from

      :func:`django.utils.timezone.now`

The default form widget for this field is a

:class:`~django.forms.TextInput`. The admin adds a JavaScript calendar,