Please add a license so that we know what we are allowed to do with the book source. As it stands, without a license, the only thing we are legally allowed to do is read the source files.
If that is your intention, I am totally fine with that and will suggest to my students that they purchase it on Amazon (as I did.)
But, the fact that you put it up on GitHub in a publicly accessible repo, with a build script, makes me wonder if you intended for people to build their own copy for their own use. If that is the case, may I suggest that you put a license on it that makes that clear?
Assuming that you do not want anyone else selling the book, I suggest CC-BY-NC-ND if you don't want others to be able to modify and redistribute it, or CC-BY-NC-SA if you want to allow others to modify and redistribute it.
Thank you for considering this.