Added learning material by Nicholas C. Zakas

Author: Abhijeet.N.Mishra

README.md

@@ -97,4 +97,4 @@ ECMAScript 5 equivalents.
     - [First Steps with ECMAScript 6](http://exploringjs.com/es6/ch_first-steps.html) (by Axel Rauschmayer)
     - [JS Features](http://jsfeatures.in/) (by Hemanth.HM)
     - [Minimalist examples of ES6 functionalities](https://github.com/hemanth/paws-on-es6) (by Hemanth.HM)
-
+    - [Understanding ECMAScript 6](https://leanpub.com/understandinges6/read/) (by Nicholas C. Zakas)