It could be great to add the raw license on GitHub to know the used license from the repository in a standard manner. Next to it in the textbook, the section « Open Source Licensing » may be confusing, as you may expect to find things around open source licensing. A title like license alone or book license may be more appropriate ?
I'm not sure that the link between the book and the GitHub repository has been made. If it exists, it's not obvious. Could be great to have a better relation between them to have an easier navigation between the book and the repo.