Add "Auditing your Node.js modules" post

`npm install` needs to be run first. Changed it to this:

> Before we can create a shrinkwrap file, we first need to install all
> dependencies of your project by using `npm install`. Then, using the `npm shrinkwrap`
> command will create a npm-shrinkwrap.json file. Be sure to keep your
> shrinkwrap file up-to-date when adding, updating or removing modules.