Document interaction with Swift Argument Parser

I have been using `ArgumentParser` in my projects to allow having multiple commands like `http-service` or `smoke-test`, etc. This makes me curious: How would I bridge the gap between `swift-configuration` and `swift-argument-parser` providing me with a way to use both in my project?

No files, tests, or entry points are named. Start by reviewing the swift-configuration documentation and the Swift Argument Parser integration question in this issue; document how projects can use both packages with multiple commands, with completion defined by a clear, usable integration guide.

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