Document the limitations on foreign keys and m2m relations across databases
|Reported by:||Russell Keith-Magee||Owned by:||nobody|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
Many of the people investigating the new multi-db functionality are coming back to django-users and django-dev asking why they can't have a foreign key to an object on a remote database. We need to specifically document that this isn't possible (and why it isn't possible).