Update index.rst (#968)

Adds introductory context and links to the PyTorch Libraries to audio docs.

docs/source/index.rst

 torchaudio
 ==========
+This library is part of the `PyTorch
+<http://pytorch.org/>`_ project. PyTorch is an open source
+machine learning framework.
+
+Features described in this documentation are classified by release status:
+
+  *Stable:*  These features will be maintained long-term and there should generally
+  be no major performance limitations or gaps in documentation.
+  We also expect to maintain backwards compatibility (although
+  breaking changes can happen and notice will be given one release ahead
+  of time).
+
+  *Beta:*  Features are tagged as Beta because the API may change based on
+  user feedback, because the performance needs to improve, or because
+  coverage across operators is not yet complete. For Beta features, we are
+  committing to seeing the feature through to the Stable classification.
+  We are not, however, committing to backwards compatibility.
+
+  *Prototype:*  These features are typically not available as part of
+  binary distributions like PyPI or Conda, except sometimes behind run-time
+  flags, and are at an early stage for feedback and testing.
+  
 
 The :mod:`torchaudio` package consists of I/O, popular datasets and common audio transformations.
 
@@ -17,3 +39,16 @@ The :mod:`torchaudio` package consists of I/O, popular datasets and common audio
    compliance.kaldi
    kaldi_io
    utils
+   
+   
+.. toctree::
+   :maxdepth: 1
+   :caption: PyTorch Libraries
+
+   PyTorch <https://pytorch.org/docs>
+   torchaudio <https://pytorch.org/audio>
+   torchtext <https://pytorch.org/text>
+   torchvision <https://pytorch.org/vision>
+   TorchElastic <https://pytorch.org/elastic/>
+   TorchServe <https://pytorch.org/serve>
+   PyTorch on XLA Devices <http://pytorch.org/xla/>