Nostr pubkey alias map

Related to #74. I'm trying to run my own instance connected to just my relay.

I'd like to have a friendlier username on the Fediverse side. Currently I just added this to transmutate.js:

const userName = "8685ebef665338dd6931e2ccdf3c19d9f0e5a1067c918f22e7081c2558f8faf8" ? "sjors" : event.pubkey;

It would be nice if I don't have to maintain that as a patch. Perhaps a map could be passed in with ALIAS_MAP=hex:username,hex:username? You could even make that a premium feature on mostr.pub.