Mention consequences of enabling `macOSPrivateApi`

[JonasKruckenberg]

According to @lucasfernog one can still notarize an app using macOS private APIs, but will be rejected from the App Store.

[simonhyll]

This is an upstream issue as the fix would be to update the official documentation in the configuration itself, which in turn would fix the docs. I'll track it for 2.0 for now just so I dont forget fixing it upstream.