Improve error message if a required argument is missing

Current situation

If a command line argument is missing, there is an error message but it is not helpfull:

$ opentf-ctl get workflow
ERROR:root:Unknown command.  Use --help to list known commands.

Desired outcome

Something like the following would be better:

$ opentf-ctl get workflow
ERROR:root:Missing required parameter.  Use "get workflow --help" for details.