[1.7.x] Note re migrations importing custom fields
[1.7.x] Note re migrations importing custom fields

Backport of b4d486c80f from master

oscaro/django,jyotsna1820/django,oscaro/django,jyotsna1820/django,jyotsna1820/django,oscaro/django,jyotsna1820/django,oscaro/django