Implement the CLI

This issue depends on #17 (closed) .

Implement the CLI based on the specification in the design statement. In case something changed about the usage of the CLI, modify the README.md accordingly.

The CLI does not have to be complicated, I assume it can be done in about 100 lines of python code. I doubt any classes will be needed.

Consider using the libraries linked in the discord, e.g. a JWT library and a library to parse the configuration files (e.g. json, yaml)