Update README.md

Author: lestrrat

README.md

@@ -192,11 +192,11 @@ This project is licensed under the MIT License - see the [LICENSE](LICENSE) file
 
 ## Related Projects
 
-- [github.com/lestrrat-go/sfv](https://github.com/lestrrat-go/sfv) - Structured Field Values (RFC 8941)
+- [github.com/lestrrat-go/sfv](https://github.com/lestrrat-go/sfv) - Structured Field Values (RFC 9561)
 - [github.com/lestrrat-go/dsig](https://github.com/lestrrat-go/dsig) - Digital Signatures for Go
 
 ## References
 
 - [RFC 9421: HTTP Message Signatures](https://www.rfc-editor.org/rfc/rfc9421.html)
 - [RFC 8941: Structured Field Values](https://www.rfc-editor.org/rfc/rfc8941.html)
-- [HTTP Message Signatures IANA Registry](https://www.iana.org/assignments/http-message-signatures/)
+- [HTTP Message Signatures IANA Registry](https://www.iana.org/assignments/http-message-signatures/)