Oh thanks! I've switched the top URL to that now. Submitted URL was https://github.com/datascale-ai/data_engineering_book.

I hope xx123122 won't mind my mentioning that they emailed us about this post, which originally got caught in a spam filter. I invited them to post a comment giving the background to the project but they probably haven't seen my reply yet. Hopefully soon, given that the post struck a chord!