[1.7.x] Fixed clone URL of Django git repository.

Backport of 905c4fdcc3 from master
[1.7.x] Fixed #23075 -- Added documentation on novalidate attribute and made it default for admin

Backport of cbdda28208c9c2aea479d5a482ff27bf37869d34 from master.
[1.7.x] Fixed #23354 -- Documented that ModelChoiceField to_field_name should be a unique field.

Thanks Keryn Knight for the suggestion.

Backport of 83762da3fb from master
[1.7.x] Documented --database option for migrate.

Thanks Mike O'Connor for the reporty.

Backport of 6aae07fe61 from master