Add https://johnnygizmo.github.io/extensions/index.json to your Blender add-on repository list to access these extensions through Blender's add-on manager..
Open the Preferences window in Blender, navigate to the Add-ons section
In the Repositories tab, click the "+" button to add a new repository.
Enter the URL https://johnnygizmo.github.io/extensions/index.json and click "Create".
Search for "Rigging"... The extensions will now appear in the Add-ons section, ready to be installed