Adding contributing guide

Author: Kent C. Dodds

README.md

@@ -77,6 +77,17 @@ var App = React.createClass({
 React.renderComponent(<App/>, document.body);
 ```
 
+## Contributing
+
+- Fork the project
+- `$ npm install && npm run build`
+- Make changes, webpack will watch and rebuild as you make changes
+- Add appropriate tests
+- `$ npm run test`
+- If tests don't pass, make them pass.
+- Update README with appropriate docs.
+- Commit and PR
+
 ## License
 
 MIT