Hi! Thanks for your purchase :)
You can find a pdf with the documentation at the root of the package: documentation.pdf
And there's a demo scene with code examples at: Scenes/DemoQTE and the class QTEDemoRunner shows you how to use.
Once you add the prefab of a QTE in the scene, be sure to make it work by calling:
QTE.OnFail.AddListener(callback);
QTE.OnSuccess.AddListener(callback);
QTE.ShowQTE(position, scale, difficulty);
If you are trying to use the QTEDemoRunner class directly, don't forget to link the prefab in the inspector, and to call the function Show()