Create a ``desc`` node summarizing the class docstring.

def _format_class_nodes(self, task_class):
        """Create a ``desc`` node summarizing the class docstring.
        """
        # Patterned after PyObject.handle_signature in Sphinx.
        # https://github.com/sphinx-doc/sphinx/blob/3e57ea0a5253ac198c1bff16c40abe71951bb586/sphinx/domains/python.py#L246

        modulename = task_class.__module__
        classname = task_class.__name__
        fullname = '.'.join((modulename, classname))

        # The signature term
        signature = Signature(task_class, bound_method=False)
        desc_sig_node = self._format_signature(
            signature, modulename, classname, fullname, 'py:class')

        # The content is the one-sentence summary.
        content_node = desc_content()
        content_node += self._create_doc_summary(task_class, fullname,
                                                 'py:class')

        desc_node = desc()
        desc_node['noindex'] = True
        desc_node['domain'] = 'py'
        desc_node['objtype'] = 'class'
        desc_node += desc_sig_node
        desc_node += content_node
        return desc_node