update readme

Author: lzhfe

README.md

@@ -1,7 +1,7 @@
 ### Usage
 - Clone or fork this repository
-- Make sure you have [node.js](https://nodejs.org/) installed
-- run `npm install -g webpack webpack-dev-server typings typescript` to install global dependencies
+- Make sure you have [node.js](https://nodejs.org/) installed（>= 6.0）
+- run `npm install -g webpack webpack-dev-server typescript` to install global dependencies
 - run `npm install` to install dependencies
 - run `npm start` to fire up dev server
 - open browser to [`http://localhost:3000`](http://localhost:3000)