Add a note about data field being removed if USE_JSONFIELD is not True.
Add a note about data field being removed if USE_JSONFIELD is not True.

See https://github.com/sphinx-doc/sphinx/issues/3213 for discussion.

thelabnyc/django-activity-stream,thelabnyc/django-activity-stream,pombredanne/django-activity-stream,justquick/django-activity-stream,justquick/django-activity-stream,pombredanne/django-activity-stream