code: def add_channel(self, title, source_id, domain, language, description=None, thumbnail=None):
          
          string_buffer = StringIO()
          writer = csv.writer(string_buffer, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)
          writer.writerow(['Title', 'Description', 'Domain', 'Source ID', 'Language', 'Thumbnail'])
          writer.writerow([title, description, domain, source_id, language, thumbnail])
          self.zf.writestr('Channel.csv', string_buffer.getvalue())
docs: add_channel: Creates channel metadata
              Args:
                  source_id: (str) channel's unique id
                  domain: (str) who is providing the content (e.g. learningequality.org)
                  title: (str): name of channel
                  language: (str): language code for channel (e.g. 'en')
                  description: (str) description of the channel (optional)
                  thumbnail: (str) path to thumbnail in zip (optional)
              Returns: None