Returns an instance of :class:`ScissorsBuilder` from the SIGRES file.

        Raise:
            `RuntimeError` if SIGRES file is not found.

def get_scissors_builder(self):
        """
        Returns an instance of :class:`ScissorsBuilder` from the SIGRES file.

        Raise:
            `RuntimeError` if SIGRES file is not found.
        """
        from abipy.electrons.scissors import ScissorsBuilder
        if self.sigres_path:
            return ScissorsBuilder.from_file(self.sigres_path)
        else:
            raise RuntimeError("Cannot find SIGRES file!")