Option to Wrap App from Local Folder Instead of URL

**Is your feature request related to a problem? Please describe.**

I think some people like me would enjoy the feature of being able to wrap your PWA from the source for testing purposes before putting it live on the web.

**Describe the solution you'd like**

As a end-user of this, I would appreciate the ability to be able to wrap an app from a local folder instead of URL for beta testing and the such, so that I know that my project works before putting it online. It would also be pretty useful too, and will allow the app the work offline instead of always having to be online.

**Describe alternatives you've considered**

I have tried using `file:///` URI scheme/method to locate my manifest locally, but unfortunately your application says it lacks the support for it.