demo app: local file/share support

[ohthehugemanatee]

The demo app is already very useful and offers one of the only open source, non invasive options for local transcription on the app store.

Could we add the capability to open arbitrary audio files and/or accept them via app share?

[guyluz11]

I was expecting to have a button to choose a file from my device. Just added a review on the app store saying it was missing. We'd love to remove it whenever this feature is added because it is basic feature of using Whisper.