Create CONTRIBUTING.md

Author: mfix22

.github/CONTRIBUTING.md

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+# Contributing
+
+1. [Fork](https://help.github.com/articles/fork-a-repo/) this repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository/) it locally
+2. Install the dependencies: `npm install` or `yarn`
+3. Run `npm link` or `yarn link` to link the scripts found in `bin` for testing terminal commands
+4. Before submitting a pull request, run `npm test` or `yarn test`