Remove obsolete note in README.
Remove obsolete note in README.

We now work around the limitation by poking at the internal data structures to
preserve any prior ``select_related`` calls.

carljm/django-model-utils,yeago/django-model-utils,kezabelle/django-model-utils,patrys/django-model-utils,yeago/django-model-utils,kezabelle/django-model-utils,nemesisdesign/django-model-utils,timmygee/django-model-utils,timmygee/django-model-utils,patrys/django-model-utils,nemesisdesign/django-model-utils,carljm/django-model-utils