Add COSE-HPKE to the references in README.

Author: dajiaji

README.md

@@ -13,6 +13,7 @@ implementation compliant with:
 - [RFC9053: CBOR Object Signing and Encryption (COSE): Initial Algorithms](https://www.rfc-editor.org/rfc/rfc9053.html)
 - [RFC9338: CBOR Object Signing and Encryption (COSE): Countersignatures](https://www.rfc-editor.org/rfc/rfc9338.html) - experimental
 - [RFC8392: CWT (CBOR Web Token)](https://tools.ietf.org/html/rfc8392)
+- [draft-04: Use of HPKE with COSE](https://www.ietf.org/archive/id/draft-ietf-cose-hpke-04.html) - experimental
 - and related various specifications. See [Referenced Specifications](#referenced-specifications).
 
 It is designed to make users who already know about [JWS](https://tools.ietf.org/html/rfc7515)/[JWE](https://tools.ietf.org/html/rfc7516)/[JWT](https://tools.ietf.org/html/rfc7519)
@@ -1666,12 +1667,13 @@ Python CWT is (partially) compliant with following specifications:
 
 - [RFC9052: CBOR Object Signing and Encryption (COSE): Structures and Process](https://www.rfc-editor.org/rfc/rfc9052.html)
 - [RFC9053: CBOR Object Signing and Encryption (COSE): Initial Algorithms](https://www.rfc-editor.org/rfc/rfc9053.html)
-- [RFC9338: CBOR Object Signing and Encryption (COSE): Countersignatures](https://www.rfc-editor.org/rfc/rfc9338.html)
+- [RFC9338: CBOR Object Signing and Encryption (COSE): Countersignatures](https://www.rfc-editor.org/rfc/rfc9338.html) - experimental
 - [RFC8812: COSE and JOSE Registrations for Web Authentication (WebAuthn) Algorithms](https://tools.ietf.org/html/rfc8812)
 - [RFC8747: Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)](https://tools.ietf.org/html/rfc8747)
 - [RFC8392: CWT (CBOR Web Token)](https://tools.ietf.org/html/rfc8392)
 - [RFC8230: Using RSA Algorithms with COSE Messages](https://tools.ietf.org/html/rfc8230)
 - [RFC8152: CBOR Object Signing and Encryption (COSE)](https://tools.ietf.org/html/rfc8152)
+- [draft-04: Use of HPKE with COSE](https://www.ietf.org/archive/id/draft-ietf-cose-hpke-04.html) - experimental
 - [Electronic Health Certificate Specification](https://github.com/ehn-dcc-development/hcert-spec/blob/main/hcert_spec.md)
 - [Technical Specifications for Digital Green Certificates Volume 1](https://ec.europa.eu/health/sites/default/files/ehealth/docs/digital-green-certificates_v1_en.pdf)