[1.6.x] Documented a current limitation of multiple table annotation; refs #10060.
[1.6.x] Documented a current limitation of multiple table annotation; refs #10060.

Backport of 4b23a6c7a9232cc07ec95fe98be17efbd4449822 from master

django-nonrel/django,felixjimenez/django,django-nonrel/django,felixjimenez/django,redhat-openstack/django,redhat-openstack/django,redhat-openstack/django,felixjimenez/django,felixjimenez/django,django-nonrel/django,redhat-openstack/django,django-nonrel/django