message: Update README.md
  I think there should be something under ### Resources for example:
  * Additional OpenCV functionality: <https://github.com/opencv/opencv_contrib>
diff: * Docs: <https://docs.opencv.org/master/>
  * Q&A forum: <http://answers.opencv.org>
  * Issue tracking: <https://github.com/opencv/opencv/issues>
  +* Additional OpenCV functionality: <https://github.com/opencv/opencv_contrib>
  ### Contributing
  