If you click on "Chapters" it takes you to a directory listing of the chapters, click on a chapter link and it takes you to another directory listing of pages. Click on a page link and it takes you to an actual chapter.

It appears that the "book" still needs a fair amount of polishing to be navigable.

See my reply to OP but here is the GH: https://github.com/heathermiller/dist-prog-book

Yep, the book is very much far from completion. Feel free to submit issues on GitHub if you notice specific things, or just wait until later this year for all the navigation problems to be solved. :)

Thanks! It's just surprising when the articles are decently styled.

This is actually a hosted version of this GH: https://github.com/heathermiller/dist-prog-book

They highlight that the hosted site is far from polished but you can always host it yourself ;)