message: Added link to CONTRIBUTING.md file in README.md
diff: @@ -292,7 +292,7 @@ Tink is maintained by:
  ## Contact and mailing list
  -If you want to contribute, please read CONTRIBUTING and send us pull requests.
  +If you want to contribute, please read [CONTRIBUTING](https://github.com/google/tink/blob/master/CONTRIBUTING.md) and send us pull requests.
  You can also report bugs or request new tests.
  If you'd like to talk to our developers or get notified about major new tests,
  