Update index.rst (Lightning-AI#2870)

Author: edenlightning

docs/source/index.rst

@@ -63,6 +63,7 @@ PyTorch Lightning Documentation
    :name: Tutorials
    :caption: Tutorials
 
+   PyTorch Lightning 101 class <https://www.youtube.com/playlist?list=PLaMu-SDt_RB5NUm67hU2pdE75j6KaIOv2>
    From PyTorch to PyTorch Lightning <https://towardsdatascience.com/from-pytorch-to-pytorch-lightning-a-gentle-introduction-b371b7caaf09>
    Video on how to refactor PyTorch into PyTorch Lightning <https://www.youtube.com/watch?v=QHww1JH7IDU>