I found this whole section quite a mouth full, and it took me a few reads to "get it". I think it could be simplified by leaving out some detail that could be implied. Something like the below perhaps?

"Note that it is also possible to order a queryset by a related field, without incurring the cost of a JOIN, by referring to the ``id`` of the related field::

    # No Join
    Entry.objects.order_by('blog_id')

    # Join
    Entry.objects.order_by('blog')