[1.4.X] Fixed #17435 - Clarified that QuerySet.update returns the number of rows matched

.. method:: update(**kwargs)

Performs an SQL update query for the specified fields, and returns

the number of rows affected.

the number of rows matched (which may not be equal to the number of rows

updated if some rows already have the new value).

For example, to turn comments off for all blog entries published in 2010,

you could do this::

    >>> Entry.objects.all().update(blog=b)

The ``update()`` method is applied instantly and returns the number of rows

affected by the query. The only restriction on the

matched by the query (which may not be equal to the number of rows updated if

some rows already have the new value). The only restriction on the

:class:`~django.db.models.query.QuerySet` that is updated is that it can only

access one database table, the model's main table. You can filter based on

related fields, but you can only update columns in the model's main