[1.9.x] Fixed #26239 -- Added a note about how auto_now works with QuerySet.update().

    for "last-modified" timestamps. Note that the current date is *always*

    used; it's not just a default value that you can override.

    The field is only automatically updated when calling :meth:`Model.save()

    <django.db.models.Model.save>`. The field isn't updated when making updates

    to other fields in other ways such as :meth:`QuerySet.update()

    <django.db.models.query.QuerySet.update>`, though you can specify a custom

    value for the field in an update like that.

.. attribute:: DateField.auto_now_add

    Automatically set the field to now when the object is first created. Useful