subcommandTerm(cmd) {
    // Legacy. Ignores custom usage string, and nested commands.
    const args = cmd.registeredArguments
      .map((arg) => humanReadableArgName(arg))
      .join(' ');
    return (
      cmd._name +
      (cmd._aliases[0] ? '|' + cmd._aliases[0] : '') +
      (cmd.options.length ? ' [options]' : '') + // simplistic check for non-help option
      (args ? ' ' + args : '')
    );
  }
Get the command term to show in the list of subcommands.

@param {Command} cmd
@returns {string}