Improve help display for commands with no arguments
Improve help display for commands with no arguments

For commands that take no positional arguments, don't display
`[arguments...]`.

Assume that if a command has a nil ArgsUsage, it is configured as such.

luizbranco/torus-cli,manifoldco/torus-cli,manifoldco/torus-cli,manifoldco/torus-cli,luizbranco/torus-cli,luizbranco/torus-cli