[1.5.X] Fixed #20513 - Expanded docs on QuerySet caching.
[1.5.X] Fixed #20513 - Expanded docs on QuerySet caching.

Thanks seddonym.

Backport of 8365d76da0 from master

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