def add_url(self, url, description=None):
        """Add a personal website.

        Args:
            :param url: url to the person's website.
            :type url: string

            :param description: short description of the website.
            :type description: string
        """
        url = {
            'value': url,
        }
        if description:
            url['description'] = description
        self._append_to('urls', url)