code: def _add_to_download_queue(self, lpath, rfile):
          # type: (Downloader, pathlib.Path,
          #        blobxfer.models.azure.StorageEntity) -> None
          
          # prepare remote file for download
          dd = blobxfer.models.download.Descriptor(
              lpath, rfile, self._spec.options, self._general_options,
              self._resume)
          with self._transfer_lock:
              self._transfer_cc[dd.entity.path] = 0
              if dd.entity.is_encrypted:
                  self._dd_map[str(dd.final_path)] = dd
          # add download descriptor to queue
          self._transfer_queue.put(dd)
          if self._download_start_time is None:
              with self._transfer_lock:
                  if self._download_start_time is None:
                      self._download_start_time = blobxfer.util.datetime_now()
docs: Add remote file to download queue
          :param Downloader self: this
          :param pathlib.Path lpath: local path
          :param blobxfer.models.azure.StorageEntity rfile: remote file