No `book-src` directory

[Steffo99]

Seems like it was accidentaly deleted in ed6ae32... 😅

[Lokathor]

Unfortunately, I didn't really have the time to update and maintain the book text, specifically the code sample snippits of the setup process. If you'd like to do that I could merge it and get github pages publishing the book again. Until then things are "probably good enough" as long as the examples build and run, which they did the last time i checked.