add npm build script and update the doc accordingly

README.md

@@ -34,8 +34,8 @@ To run the app from source, just clone the code and run this in your terminal:
 
 ```
 npm install
-grunt
+npm run build
-./index.js --port 8080
+npm start -- --port 8080
 ```
 
 And if you don't have [grunt](http://gruntjs.com/getting-started) installed already, just run `npm install -g grunt-cli`.

package.json

@@ -13,6 +13,7 @@
   },
   "scripts": {
     "start": "node index",
+    "build": "grunt",
     "test": "HOME=test/fixtures mocha test/**/*.js"
   },
   "keywords": [