No, really: Invite anyone to your tailnet

Right around the turn of the new year, we rolled out a little update to our user invite system. The change: you can now invite people who don't authenticate through GitHub to join a tailnet owned by a user who does. For users who have built out tailnets based on a GitHub login and had run into this issue, it's a small headache relieved. But it also reflects a bigger milestone — we were finally able to remove the "limitations" section from our "Invite any user" documentation.