move/duplicate the `npm install` section of "deploying your app" to user-guide

I was following the user-guide converting my app to fastboot. I got trolled hard by the "you have to run `npm install` in the dist folder" so your express server can run the modules. Probably because that section was in the "deploying your app" section, and I was still trying to get it running locally, so I hadn't read that far ahead yet.

I think this nugget should be earlier in the docs.