Add 'npm start' script

Author: Limon Monte

Diff for: README.md

@@ -100,7 +100,7 @@ To use the Material theme, import the correspondent file from the `theme/materia
 
 1. When in the `vaadin-button` directory, run `npm install` and then `bower install` to install dependencies.
 
-1. Run `polymer serve --open`, browser will automatically open the component API documentation.
+1. Run `npm start`, browser will automatically open the component API documentation.
 
 1. You can also open demo or in-browser tests by adding **demo** or **test** to the URL, for example:
 

Diff for: package.json

@@ -24,6 +24,8 @@
   ],
   "scripts": {
     "test": "wct",
+    "prestart": "polymer analyze vaadin-* > analysis.json",
+    "start": "polymer serve --open",
     "preversion": "gulp version:update"
   },
   "devDependencies": {