message: Add a link to Proxygen in Mvfst README for HTTP/3
  Summary:
  People have been looking for and asking HTTP/3 code in Mvfst repo. I
  think a link here will clarify this.
diff: @@ -109,6 +109,9 @@ For more options, see
  ```
  ./_build/build/quic/samples/echo --help
  ```
  +## HTTP/3
  +This repo implements the QUIC trasnport. For an HTTP/3 implementation that uses Mvfst, please check out [Proxygen](https://github.com/facebook/proxygen).
  +
  ## Contributing
  We'd love to have your help in making `mvfst` better. If you're interested, please
  