Way to emit help message that includes non-option arguments

[MikeTaylor]

The help message that's autogenerated from the options is of the form

Usage:
  node myprog [OPTION]

Options:
  -v, --verbose Verbose mode
  [etc.]

But often the usage of myprog includes other, non-option, arguments, such as a filename to read. So I'd like the first part to read (say) Usage: node myprog [OPTION] <filename>.

It would be nice to have a simpler way to do this than by copying the default this.help value from the source, modifying it as needed and feeding it to setHelp.

Maybe something like a setHelpExtraArgs('<filename>')?