Add CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,31 @@
+### Setup up your dev environment
+
+1. Fork the repo and create your branch from `master`.
+   A guide on how to fork a repository: https://help.github.com/articles/fork-a-repo/
+
+   Open terminal (e.g. Terminal, iTerm, Git Bash or Git Shell) and type:
+   ```sh
+   git clone https://github.com/<your_username>/jest-runner-mocha
+   cd jest
+   git checkout -b my_branch
+   ```
+   Note:
+   Replace `<your_username>` with your GitHub username
+
+2. jest-runner-mocha uses [Yarn](https://code.facebook.com/posts/1840075619545360)
+   for running development scripts. If you haven't already done so,
+   please [install yarn](https://yarnpkg.com/en/docs/install).
+
+3. Run `yarn`.
+
+     ```sh
+    yarn
+    ```
+
+5. If you've changed APIs, update the documentation.
+
+6. Ensure the test suite passes via `yarn test`. To run the test suite you
+
+   ```sh
+   yarn test
+   ```