message: add link to slack
diff: @@ -27,6 +27,10 @@ cloud computing applications. It is the result of a research project at RWTH
  Aachen University and is currently an experimental approach, i.e., not
  production ready. Please use it with caution.
  +## Contributing
  +
  +HermitCore is being developed on [GitHub](https://github.com/RWTH-OS/HermitCore).
  +Create your own fork, send us a pull request, and chat with us on [Slack](https://radiant-ridge-95061.herokuapp.com).
  ## Requirements
  