Update README.md (#167)

Added a link for learning ES6 syntax on Codecademy

Author: pulamusic

README.md

@@ -94,6 +94,7 @@ Spend a day or two revising ES5 and exploring ES2015. The more heavily used feat
 #### Study Links
 
 - [Learn ES5 on Codecademy](https://www.codecademy.com/learn/learn-javascript)
+- [Learn ES6 on Codecademy](https://www.codecademy.com/learn/introduction-to-javascript)
 - [Learn ES2015 on Babel](https://babeljs.io/learn-es2015/)
 - [ES6 Katas](http://es6katas.org/)
 - [You Don't Know JS](https://github.com/getify/You-Dont-Know-JS) (Advanced content, optional for beginners)