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

def main_help_text(self, commands_only=False):
        """
        Returns the script's main help text, as a string.
        """
        if commands_only:
            usage = sorted(get_commands().keys())
        else:
            usage = [
                "",
                "Type '%s help <subcommand>' for help on a specific subcommand." % self.prog_name,
                "",
                "Available subcommands:",
            ]
            commands_dict = collections.defaultdict(lambda: [])
            for name, app in six.iteritems(get_commands()):
                if app == 'pug.crawlnmine':
                    app = 'pug'
                else:
                    app = app.rpartition('.')[-1]
                commands_dict[app].append(name)
            style = color_style()
            for app in sorted(commands_dict.keys()):
                usage.append("")
                usage.append(style.NOTICE("[%s]" % app))
                for name in sorted(commands_dict[app]):
                    usage.append("    %s" % name)
            # Output an extra note if settings are not properly configured
            if self.settings_exception is not None:
                usage.append(style.NOTICE(
                    "Note that only Django core commands are listed "
                    "as settings are not properly configured (error: %s)."
                    % self.settings_exception))

        return '\n'.join(usage)