Allow usage from self-hosted Standard Notes instances

[PeterCxy]

Commit c366bbb removed the possibility to use Listed from self-hosted Standard Notes servers because it is impossible to create new authors directly from a self-hosted server. Before c366bbb, one would simply go to the new-authors page and get a author link that way, but after that commit it is now completely impossible to create new authors unless one uses the official Standard Notes server.

It would be nice to bring back this possibility, even if it is hidden under some FAQ item instead of being the default behavior as it was before.