Quick prototype of creating a book format

*Please do not merge*

We have been asked for a pdf version of the service manual in the past. I’m
not completely sure what the user need is for this, but here is a very basic
sketch around that.

To try it out, you’ll need to install a few things:

* `sudo aptitude install node`
* `npm install gitbook`
* `npm install gitbook-pdf`

If that works, you can then create different versions of the content:

```
$ gitbook pdf ./
```