def add_cell_footer(self):
        """
        Add footer cell
        """

        # check if there's already a cell footer... if true, do not add a second cell footer.
        # this situation happens when exporting to ipynb and then importing from ipynb.

        logging.info('Adding footer cell')

        for cell in self.nb['cells']:
            if cell.cell_type == 'markdown':
                if 'pynb_footer_tag' in cell.source:
                    logging.debug('Footer cell already present')
                    return

        m = """

            ---
            * **Notebook class name**: {class_name}
            * **Notebook cells name**: {cells_name}
            * **Execution time**: {exec_begin}
            * **Execution duration**: {exec_time:.2f}s
            * **Command line**: {argv}
            [//]: # (pynb_footer_tag)
            """
        self.add_cell_markdown(
            m.format(exec_time=self.exec_time, exec_begin=self.exec_begin_dt, class_name=self.__class__.__name__,
                     argv=str(sys.argv), cells_name=self.cells_name))
Add footer cell