Netlify CMS is a content management application which uses git hosting services API (e.g. GitHub) as a backend. It hides the complexity of managing content via GitHub API from you.
It is very extendable as you can register a variety of your own React components. If you use JSX syntax and/or a styling library you probably need a build step so working from CDN is not an option.
If you register you own components via pure JS code you can work directly from CDN.
I would recommend using renovate instead of directly from CDN as you can control when new dependencies are introduced, and it is easier to share code between the CMS and your frontend.
The repo you linked uses it:
So if you forked/cloned it you probably only need to give the renovate bot access.