I suggest to config GitHub pages to host the master branch directly. That way we can directly read the site content on diveintomark.github.io/diveintopython3 without cloning.
The setting is under "Settings" > "GitHub Pages":
The default settings for publishing your site's source files depend on your site type and the branches you have in your site repository.
If your site repository doesn't have a master or gh-pages branch, your GitHub Pages publishing source is set to None and your site is not published.

After you've created either a master or gh-pages branch, you can set one as your publishing source so that your site will be published.
If you fork or upload your site repository with only a master or gh-pages branch, your site's source setting will automatically be enabled for that branch.
The result would look like this:
https://yookoala.github.io/diveintopython3/
I suggest to config GitHub pages to host the
masterbranch directly. That way we can directly read the site content on diveintomark.github.io/diveintopython3 without cloning.The setting is under "Settings" > "GitHub Pages":
The result would look like this:
https://yookoala.github.io/diveintopython3/