Create CONTRIBUTING.md

Author: another-guy

CONTRIBUTING.md

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+# Contributing
+
+Contribution is the best way to improve any project!
+
+1. Fork it!
+1. Create your feature branch (git checkout -b my-new-feature).
+1. Commit your changes (git commit -am 'Added some feature')
+1. Push to the branch (git push origin my-new-feature)
+1. Create new Pull Request
+
+...or follow steps described in a nice [fork guide](http://kbroman.org/github_tutorial/pages/fork.html) by Karl Broman