Add prerequisits to CONTRIBUTING.md (#40)

* Add prerequisitits to CONTRIBUTING.md

* Update versions and link to yarn

packages/learn/CONTRIBUTING.md

@@ -1,10 +1,16 @@
 # Contributing
 
+Prerequistits| Minimum Version
+|---|---|
+node | ^8.11.x
+[yarn](https://yarnpkg.com/en/) | ^1.3.0
+
+
 1. Fork the repo
 2. clone locally
 3. `yarn install`
 4. `git branch -b <your-branch-name>`
 5. `yarn develop`
+5. Make your changes
 6. Make a PR
 7. Bask in the glory of your accomplishments
-