Add PGP as NIP-39 external identity

39.md

@@ -20,6 +20,7 @@ A new optional `i` tag is introduced for `kind 0` metadata event contents in add
     ["i", "twitter:semisol_public", "1619358434134196225"],
     ["i", "mastodon:bitcoinhackers.org/@semisol", "109775066355589974"]
     ["i", "telegram:1087295469", "nostrdirectory/770"]
+    ["i", "pgp:A999B7498D1A8DC473E53C92309F635DAD1B5517", "xsFNBF2V8eEBEADmjYzGOpxEI0J7jQ1qFzlsrjF6NaBSq+UqKw..."]
   ],
   ...
 }
@@ -62,3 +63,9 @@ Identity: A Telegram user ID.
 
 Proof: A string in the format `<ref>/<id>` which points to a message published in the public channel or group with name `<ref>` and message ID `<id>`. This message should be sent by user ID `<identity>` and have the text `Verifying that I control the following Nostr public key: "<npub encoded public key>"`.
 This can be located at `https://t.me/<proof>`.
+
+### `pgp`
+
+Identity: A PGP fingerprint.
+
+Proof: PGP signature of the fingerprint used in the identity field.