Update cli.py to add multi-domain parsing

Options for adding multiple domains from a file or from stdin

:pushpin: References

Added a feature request for this and decided just to implement it.

:tophat: What is the goal?

More flexibility when dealing with multiple domain names.

:memo: Notes

Did not document the changes in the code.

:art: A picture is worth a thousand words

:white_check_mark: Checklist

• [ ] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked this works with manual QA