Update the CONTRIBUTING to reflect the adoption of Yarn

Author: jgonggrijp

CONTRIBUTING.md

@@ -10,28 +10,29 @@ Create your own fork of contrib where you can make your changes.
 
 ## 3. Install development dependencies
 
-Make sure you have [Node.js][node] and the [grunt cli][cli] installed. Then install contrib's development dependencies with `npm install`.
+Make sure you have [Node.js][node] and [Yarn][yarn] installed. Then install contrib's development dependencies with `yarn`. Note that these dependencies include the [Grunt CLI][cli] which we use for task automation.
 
 ## 4. Change the code
 
 Make your code changes, ensuring they adhere to the same [coding style as Underscore][style]. Do **not** edit the files in `dist/`.
 
-Make any necessary updates to the qUnit tests found in `test/`. Run `grunt test` to catch any test failures or lint issues. You can also use `grunt watch:test` to get instant feedback each time you save a file.
+Make any necessary updates to the qUnit tests found in `test/`. Run `yarn test` to catch any test failures or lint issues. You can also use `yarn grunt watch:test` to get instant feedback each time you save a file.
 
 ## 5. Update the docs
 
 Make any necessary documentation updates in `docs/`. Do **not** edit `index.html` directly.
 
-After updating the docs, run `grunt tocdoc` to rebuild the `index.html` file. Visually inspect `index.html` in your browser to ensure the generated docs look nice.
+After updating the docs, run `yarn tocdoc` to rebuild the `index.html` file. Visually inspect `index.html` in your browser to ensure the generated docs look nice.
 
 ## 6. Send a pull request
 
 Send a pull request to `documentcloud/underscore-contrib` for feedback.
 
-If modifications are necessary, make the changes and rerun `grunt test` or `grunt tocdoc` as needed.
+If modifications are necessary, make the changes and rerun `yarn test` or `yarn tocdoc` as needed.
 
 And hopefully your pull request will be merged by the core team! :-)
 
 [style]:https://github.com/documentcloud/underscore/blob/master/underscore.js
 [node]:http://nodejs.org/
-[cli]:http://gruntjs.com/getting-started#installing-the-cli
+[yarn]:https://yarnpkg.com
+[cli]:http://gruntjs.com/getting-started#installing-the-cli