Better mentioning UX for fediverse -> nostr

The Problem

Currently, if a fediverse user wants to interact with a nostr user, they have to @mention the pubkey of that user. This is less than ideal because pubkeys are not designed to be easily typed/remembered by humans. Also, as a gut feeling, their computer generated nature may lead some fediverse server admins to think they are bot/spam accounts, increasing the likelihood of them blocking the entire mostr instance. (I could be wrong there, I don't actually run a Mastodon server.)

A Potential Solution

I believe we could move to a @username#discriminator scheme, similar to Discord (before the recent switch to globally unique usernames) or Blizzard's Battle.net social functionality. In this case, we would take the nostr type 0 name as the username and a fingerprint of the pubkey as the discriminator, with a fallback to just a pubkey if no username is found.

Taking the example from the README: @28fa2c82cdf60a8c06b94f2482e5de9f92e5cd03b03140dea5e1c3dc173dbf41@mostr.pub, would become something like @exampleuser#28fa@mostr.pub.

Both Blizzard and Discord used 4 number discriminators, so I imagine the first four characters of a public key should be enough to avoid collisions, but any length could realistically be chosen.