Update README.md

Author: chris-wood

README.md

@@ -7,6 +7,42 @@ This is the working area for the individual Internet-Draft, "Hashing to Elliptic
 * [Individual Draft](https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-hash-to-curve)
 * [Compare Editor's Copy to Individual Draft](https://cfrg.github.io/draft-irtf-cfrg-hash-to-curve/#go.draft-irtf-cfrg-hash-to-curve.diff)
 
+## Reference Implementations
+
+The purpose of these implementations is for generating test vectors and enabling cross compatibility with other implementations.
+
+These implementations are for reference only. They MUST NOT be used in production systems.
+
+ - [Sage](https://github.com/cfrg/draft-irtf-cfrg-hash-to-curve/tree/master/poc)
+ - [Go](https://github.com/armfazh/h2c-go-ref): 
+     [v05](https://github.com/armfazh/h2c-go-ref/tree/v5.0.0), 
+     [v06](https://github.com/armfazh/h2c-go-ref/tree/v6.0.0), 
+     [v07](https://github.com/armfazh/h2c-go-ref/tree/v7.0.0), 
+     [v08](https://github.com/armfazh/h2c-go-ref/tree/v8.0.0),
+     **[v12](https://github.com/armfazh/h2c-go-ref/tree/v12.0.0)**.
+ - [Rust](https://github.com/armfazh/h2c-rust-ref):
+     [v05](https://github.com/armfazh/h2c-rust-ref/tree/v5.0.0),
+     [v06](https://github.com/armfazh/h2c-rust-ref/tree/v6.0.0),
+     [v07](https://github.com/armfazh/h2c-rust-ref/tree/v7.0.0),
+     [v08](https://github.com/armfazh/h2c-rust-ref/tree/v8.0.0),
+     **[v12](https://github.com/armfazh/h2c-rust-ref/tree/v12.0.0)**.
+- [hacspec (Rust)](https://github.com/hacspec/hacspec/tree/master/examples/bls12-381-hash): BLS12-381, v13.
+
+
+## Other Implementations
+
+This is a (likely incomplete) list of other libraries that have implemented hash-to-curve per the standard.
+
+ - [libsodium](https://github.com/jedisct1/libsodium)
+ - [MIRACL Core](https://github.com/miracl/core)
+ - [pairing-plus](https://github.com/algorand/pairing-plus)
+ - [RELIC](https://github.com/relic-toolkit/relic)
+ - [Apache Milagro Crypto Library - Rust](https://github.com/apache/incubator-milagro-crypto-rust)
+ - [Zig's standard library](https://ziglang.org)
+ - [CIRCL](https://github.com/cloudflare/circl/)
+
+If you know of another library that supports a compliant hash-to-curve implementation and would like us to list it here, please open a PR.
+
 
 ## Contributing