Automatic Method
1. Open Rhino 8
2. Use PackageManager Command
3. Search for Ptarmigan. You should see this:
4. Click Install.
5. Make sure to click the check box of, "Automatically update packages when Rhino starts." This will ensure you have the correct version.
6. Restart Rhino 8.
Manual Method: (Not Recommended)
1. Download .yak file
here.
2. Double click or drag-and-drop into Rhino 8.
3. Restart Rhino 8.