Include description to subparser help text

[ewu63]

Description

The add_subparsers function accepts both help and description. My understanding is that help is displayed at the main parser level, and description is a longer..description displayed at the subparser level. It would be good to have both shown, and we can do this by defining the help string as a variable, then appending to it some more detailed description and passing that to description=.

Note that this has certain implications if we plan to add sphinx documentation and use autoprogram or equivalent to document the CLI.