Create CONTRIBUTING.md (#9)

Author: ckaznocha

CONTRIBUTING.md

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+# Contributing
+Enhancements or fixes are welcome
+
+## Issues
+Check if a ticket for your issue already exists in GitHub issues. If you don't
+find a ticket submit a new one.
+
+## Pull Requests
+1. Fork the repo
+1. Make your changes.
+1. Commit and push the to your fork.
+    1. Extra credit if you squash your commits first.
+1. Submit a pull request.
+
+### Style
+- Your code should pass golint.
+- Follow the existing conventions.
+
+### Tests
+- If you add any functionality be sure to also add a test for it.
+- All regressions need to pass before your pull can be accepted
+
+## License
+By contributing to intrange you agree that your contributions will be
+licensed under its MIT license.