FR: command to list supported models

[dbieber]

Feature request: add a command that lists the supported models

The tool accepts argument -m but does not seem to have a way to see what model names are valid.
The github page lists the valid model names, but I expect the list of valid names will grow with future versions of ttok.

So a command to list valid models would make it possible to figure out what model names are valid regardless of the version being run.