The turtorial article link is no longer available

The tutorial article about the [BasicSkeleton](https://github.com/autodesk-platform-services/aps-extensions/tree/main/public/extensions/BasicSkeleton) Extension [here](https://github.com/autodesk-platform-services/aps-extensions/tree/main/public/extensions/BasicSkeleton) is not available.
Is there any other tutorial or document about the structure of this kind of viewer extension?