Add list of books available at source{d} to the guide

[marnovo]

As mentioned by @eiso at src-d/office:

@estherrgarcia could we add a list of books that we [have] at source{d} to the guide.

[eiso]

Closing this issue, since you can now find the book list here: https://github.com/src-d/guide/blob/master/office/books_list.md