About Output Files in Xcode10 or later

[usk2000]

Hi, @ishkawa

I'm using your library in product and CI. I noticed that it always fails building in CI.

To use this library in Xcode 10 (or above) and CI, I use output files like "$SRCROOT/AppResolver.generated.swift" in Run Script phases, which also done in R.swift.

Please add about "Output Files" to README.

Thanks!