Create a ``desc`` node summarizing a method docstring.

def _format_method_nodes(self, task_method, modulename, classname):
        """Create a ``desc`` node summarizing a method docstring.
        """
        methodname = task_method.__name__
        fullname = '.'.join((modulename, classname, methodname))

        # The signature term
        signature = Signature(task_method, bound_method=True)
        desc_sig_node = self._format_signature(
            signature, modulename, classname, fullname, 'py:meth')

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

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