'Returns the script\'s main help text, as a string.'

def main_help_text(self):

    usage = ['', ("Type    '%s    help    <subcommand>'    for    help    on    a    specific    subcommand." % self.prog_name), '']
    usage.append('Available    subcommands:')
    commands = get_commands().keys()
    commands.sort()
    for cmd in commands:
        usage.append(('        %s' % cmd))
    return '\n'.join(usage)
