Returns a help string for a given module.

def _render_module_flags(self, module, flags, output_lines, prefix=''):
    """Returns a help string for a given module."""
    if not isinstance(module, str):
      module = module.__name__
    output_lines.append('\n%s%s:' % (prefix, module))
    self._render_flag_list(flags, output_lines, prefix + '  ')