[1.1.X] Fixed #12859 -- Clarified the documentation on using multiple tables...

You can only set non-relation fields and ``ForeignKey`` fields using this

method. To update a non-relation field, provide the new value as a constant.

To update ``ForeignKey`` fields, set the new value to be the new model

instance you want to point to. Example::

instance you want to point to. For example::

    >>> b = Blog.objects.get(pk=1)

The ``update()`` method is applied instantly and doesn't return anything

(similar to ``delete()``). The only restriction on the ``QuerySet`` that is

updated is that it can only access one database table, the model's main

table. So don't try to filter based on related fields or anything like that;

it won't work.

table. You can filter based on related fields, but you can only update columns

in the model's main table. Example::

    >>> b = Blog.objects.get(pk=1)

    # Update all the headlines belonging to this Blog.

    >>> Entry.objects.select_related().filter(blog=b).update(headline='Everything is the same')

Be aware that the ``update()`` method is converted directly to an SQL

statement. It is a bulk operation for direct updates. It doesn't run any