Looks like this is a meta tool for building skills themselves rather than using them. The repository is from Microsoft's Azure skills collection, but there's no SKILL.md documentation available, which is ironic given the name. Without docs, it's hard to say exactly what it does, but the name suggests it helps you create or manage skill definitions for Claude. If you're building custom skills or contributing to the Azure skills repo, this might be your starting point. That said, the lack of documentation makes it tough to recommend unless you're already deep in the Microsoft Azure skills ecosystem and know what you're looking for.
npx skills add https://github.com/microsoft/azure-skills --skill skill-authoring