fix: add note about incorrect type hint for Movie in SlideBuilder

Author: ya7010

src/tppt/pptx/slide.py

@@ -236,6 +236,8 @@ def _register(slide: Slide) -> Movie:
             data = MovieData(type="movie", movie_file=movie_file, **kwargs)
             movie_obj = Movie(
                 cast(
+                    # NOTE: Type hint of python-pptx is incorrect. Expected Movie, but GraphicFrame is returned.
+                    # Ref: https://github.com/scanny/python-pptx/pull/1057/commits/56338fa314d2c5bceb8b1756a50ed64ea8984abe
                     PptxMovie,
                     slide.to_pptx().shapes.add_movie(
                         movie_file,