[1.5.x] Fixed #19743 - Documented some limitations of contrib.auth.
[1.5.x] Fixed #19743 - Documented some limitations of contrib.auth.

Thanks Aymeric for the suggestion.

Backport of afa3e16334 from master

alx-eu/django,ccn-2m/django,hasadna/django,imtapps/django-imt-fork,bliti/django-nonrel-1.5,alx-eu/django,ccn-2m/django,hasadna/django,bliti/django-nonrel-1.5,hasadna/django,bliti/django-nonrel-1.5,ccn-2m/django,alx-eu/django,alx-eu/django,ccn-2m/django,imtapps/django-imt-fork,imtapps/django-imt-fork