`takesArguments` should change the usage text

[feinstein]

Commands have a takesArguments bool that indicates if they take any arguments. This is used only for validation, but when we print the usage for a particular Command they always show a [arguments] text at the end.

Usage: my_tool create [arguments]

If the Command doesn't take any arguments, then the usage help should reflect it.

Also, there should be a mechanism to add a helper text on how positional arguments should be used by the user, currently they only see [arguments] which doesn't tell much about what's expected by the cli.