docs: def add(self, artifact_type: ArtifactType, src_path: str,
              dst_path: str=None):
          """Add an artifact of type `artifact_type` at `src_path`.
  
          `src_path` should be the path of the file relative to project root.
          `dst_path`, if given, is the desired path of the artifact in dependent
          targets, relative to its base path (by type).
          """
          if dst_path is None:
              dst_path = src_path
          other_src_path = self._artifacts[artifact_type].setdefault(
              dst_path, src_path)
          if src_path != other_src_path:
              raise RuntimeError(
                  '{} artifact with dest path {} exists with different src '
                  'path: {} != {}'.format(artifact_type, dst_path, src_path,
                                          other_src_path))