[1.7.x] Documented --database option for migrate.
[1.7.x] Documented --database option for migrate.

Thanks Mike O'Connor for the reporty.

Backport of 6aae07fe61 from master

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