Add feature where users can choose the schemes to generate

[macabeus]

Will be good a feature where the users could choose the schemes to be generated in the xcode project.

One solution is by command line argument. For example:

swift swiftplate/main.swift  # create all schemes (iOS, macOS, watchOS, tvOS)
swift swiftplate/main.swift  --ios # create schemes only for iOS
swift swiftplate/main.swift  --ios --tvos # create schemes only for iOS and tvOS

[ythecombinator]

I do agree it'd be nice to be able to choose which schemes I want to be scaffolded but, instead of using multiple flags for multiple schemes I'd rather just pass an array of them–e.g.

swift swiftplate/main.swift  -s [iOS, macOS, watchOS]
swift swiftplate/main.swift  --schemes [iOS]