message: add reference to 3rd party repository
diff: @@ -132,4 +132,8 @@ to contribute to VelocyPack. Have a look for the tag HELP_WANTED in the issue
  tracker!
  We also provide a golang version of VPack in the
  -[go-velocypack repository](https://github.com/arangodb/go-velocypack).
  +[go-velocypack repository](https://github.com/arangodb/go-velocypack) and a
  +Java version in the [java-velocypack](https://github.com/arangodb/java-velocypack).
  +
  +Additionally, there is a third party VPack implementation for
  +[PHP](https://github.com/martin-schilling/php-velocypack).
  