21.md:use relative link

RandyMcMillan · RandyMcMillan · commit 0c1dfa966195 · 2024-07-28T15:37:14.000-04:00
diff --git a/21.md b/21.md
@@ -10,7 +10,7 @@ This NIP standardizes the usage of a common URI scheme for maximum interoperabil
 
 The scheme is `nostr:`.
 
-The identifiers that come after are expected to be the same as those defined in [NIP-19](https://github.com/nostr-protocol/nips/blob/master/19.md) (except `nsec`).
+The identifiers that come after are expected to be the same as those defined in [NIP-19](19.md) (except `nsec`).
 
 ## Examples
 
