docs(contributing): Add `npm install` to build instructions

CONTRIBUTING.md

@@ -5,11 +5,12 @@ This document describes how to contribute to Batarang
 ## Installing from Source
 
 1. Clone the repository: `git clone git://github.com/angular/angularjs-batarang`
-2. Install the bower dependencies: `bower install`
-3. Build the inject script: `npm run build`
-4. Navigate to `chrome://chrome/extensions/` and enable Developer Mode.
-5. Choose "Load unpacked extension"
-6. In the dialog, open the directory you just cloned.
+2. Install the npm dependencies `npm install`
+3. Install the bower dependencies: `bower install`
+4. Build the inject script: `npm run build`
+5. Navigate to `chrome://chrome/extensions/` and enable Developer Mode.
+6. Choose "Load unpacked extension"
+7. In the dialog, open the directory you just cloned.
 
 ## Running the tests