message: Update ratelimit docs with links to reference implementation
diff: @@ -34,5 +34,4 @@ gRPC service IDL
  Envoy expects the rate limit service to support the gRPC IDL specified in
  :repo:`/source/common/ratelimit/ratelimit.proto`. See the IDL documentation for more information
  -on how the API works. In the future Lyft will open source a reference service implementation
  -written in Go.
  +on how the API works. See Lyft's reference implementation [here](https://github.com/lyft/ratelimit)
  