Multiple scan paths are not supported

[micahsnyder]

The scan command only handles one scan target.

E.g. this will fail

❯ archive scan ./*
Usage: archive scan [OPTIONS] PATH
Try 'archive scan --help' for help.

Error: Got unexpected extra arguments (./clam.zip ./CODE_OF_CONDUCT.md ./CONTRIBUTING.md ./Dockerfile ./LICENSE ./pyproject.toml ./README.md ./SECURITY.md ./src)

It would be convenient to be able to pass multiple files to be scanned. But it is also fine for now that it does not. We just need to adjust the documentation and help-message to make it clear how to use it.