Add source code for website that hosts book for easier contributions

[hamirmahal]

It might be helpful for contributors to see the source code for the website, in case we want to add a night theme, or edit the titles of .pdfs to match the name of the section, for example. The tab titles are all single.dvi for me, at least on my browser, for the sections I've looked at recently.

Also, what are your thoughts on creating a Discussions section in this repository for questions like these?