docs: add more information to installation

Readme.md

@@ -21,10 +21,22 @@ app.listen(3000)
 
 ## Installation
 
+This is a [Node.js](https://nodejs.org/en/) module available through the
+[npm registry](https://www.npmjs.com/).
+
+Before installing, [download and install Node.js](https://nodejs.org/en/download/).
+Node.js 0.10 or higher is required.
+
+Installation is done using the
+[`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):
+
 ```bash
 $ npm install express
 ```
 
+Follow [our installing guide](http://expressjs.com/en/starter/installing.html)
+for more information.
+
 ## Features
 
   * Robust routing