Print usage when no arguments are passed

[MarcusZuber]

I installed tofu on some servers and for testing if it worked I tried to start tofu without any argument (which does not make any sense, but I did not think about it). In this case, you get this error message:

Traceback (most recent call last):
  File "~/.local/bin/tofu", line 227, in main
    log_level = logging.DEBUG if args.verbose else logging.INFO
                                 ^^^^^^^^^^^^
AttributeError: 'Namespace' object has no attribute 'verbose'

This error message confused me way too long...

This commit catches the case and prints the usage message instead.