docs: add link to RFC9864

Author: panva

README.md

@@ -136,6 +136,7 @@ Please note that certain algorithms may not be available depending on the runtim
 - JSON Web Key Thumbprint URI - [RFC9278](https://www.rfc-editor.org/rfc/rfc9278)
 - JWS Unencoded Payload Option - [RFC7797](https://www.rfc-editor.org/rfc/rfc7797)
 - CFRG Elliptic Curve ECDH and Signatures - [RFC8037](https://www.rfc-editor.org/rfc/rfc8037)
+- Fully-Specified Algorithms for JOSE - [RFC9864](https://www.rfc-editor.org/rfc/rfc9864.html)
 - ML-DSA for JOSE - [draft-ietf-cose-dilithium-10](https://www.ietf.org/archive/id/draft-ietf-cose-dilithium-10.html)
 
 The algorithm implementations in `jose` have been tested using test vectors from their respective specifications as well as [RFC7520](https://www.rfc-editor.org/rfc/rfc7520).