Suggest `unload` instead of help on `stop`, or add `stop` alias

[maxproske]

Minor UX issue: I expected docker model stop to work since docker model run exists.

Should DMR print a helpful error like "docker model stop" is not a command. Did you mean "docker model unload"?, or add stop as an alias for unload?

Feel free to close this issue if conflating this with stop-runner that stops the entire runner daemon would make matters worse. It does print the help text, the user can still see unload right there.