Update README

Author: calvinl

README.md

@@ -11,6 +11,13 @@ promise that future updates will not break your existing application.**
 
 ## Get started
 
+If you have (yarn)[https://github.com/yarnpkg/yarn] installed (recommended):
+```
+yarn install
+npm start
+```
+
+Otherwise:
 ```
 npm install
 npm start