It turns out /friends pages are not my idea. The IndieWeb community has been making personal websites that link to each other for years, and their wiki already lists /friends as a kind of page you can have. Lukas Rosenstock emailed me to point this out, and I think someone over there added slashfriends.org to the wiki. I have a profile there now too. Great community. Go look.
Lukas also pointed me at rel="friend", a small attribute you can put on a link to say this is a person I actually know. Nice idea, and you should add it if you like it. I am not going to require it. The only thing you need to get listed here is a real page at yourdomain.com/friends.