Fixed #17528 -- Documented that add() and remove() with a many-to-many...

            >>> e = Entry.objects.get(id=234)

            >>> b.entry_set.add(e) # Associates Entry e with Blog b.

        In the example above, ``e.save()`` is called to perform the update.

        Using ``add()`` with a many-to-many relationship, however, will not

        call any ``save()`` methods, but rather create the relationships

        using :meth:`QuerySet.bulk_create()

        <django.db.models.query.QuerySet.bulk_create>`. If you need to execute

        some custom logic when a relationship is created, listen to the

        :data:`~django.db.models.signals.m2m_changed` signal.

    .. method:: create(**kwargs)

        Creates a new object, saves it and puts it in the related object set.

            >>> e = Entry.objects.get(id=234)

            >>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.

        Similar to :meth:`add()`, ``e.save()`` is called in the example above

        to perform the update. Using ``remove()`` with a many-to-many

        relationship, however, will delete the relationships using

        :meth:`QuerySet.delete()<django.db.models.query.QuerySet.delete>` which

        means no model ``save()`` methods are called; listen to the

        :data:`~django.db.models.signals.m2m_changed` signal if you wish to

        execute custom code when a relationship is deleted.

        For :class:`~django.db.models.ForeignKey` objects, this method only

        exists if ``null=True``. If the related field can't be set to ``None``

        (``NULL``), then an object can't be removed from a relation without