Introduce IO section to getting started tutorials (#2703)

Summary:
Since that new tutorials for StreamWriter are being added, there are more tutorials for media IO than the rest.
So this commit introduces sub-index for IO tutorials.

Pull Request resolved: https://github.com/pytorch/audio/pull/2703

Reviewed By: carolineechen

Differential Revision: D39769049

Pulled By: mthrok

fbshipit-source-id: 19a3981bc624fdce1d5d703c67e28a751a15e812

docs/source/index.rst

@@ -72,9 +72,7 @@ Getting Started
    :maxdepth: 1
    :caption: Getting Started
 
-   tutorials/audio_io_tutorial
-   tutorials/streaming_api_tutorial
-   tutorials/streaming_api2_tutorial
+   tutorials.io
    tutorials/audio_resampling_tutorial
    tutorials/audio_data_augmentation_tutorial
    tutorials/audio_feature_extractions_tutorial
@@ -88,7 +86,6 @@ Advanced Usages
    :maxdepth: 1
    :caption: Advanced Usages
 
-   hw_acceleration_tutorial
    tutorials/speech_recognition_pipeline_tutorial
    tutorials/online_asr_tutorial
    tutorials/device_asr

docs/source/io.rst

+.. py:module:: torchaudio.io
+
 torchaudio.io
 =============
 

docs/source/tutorials.io.rst

+Media IO
+========
+
+TorchAudio project has started as a simple audio IO library for PyTorch, which are
+:py:func:`torchaudio.info`, :py:func:`torchaudio.load` and :py:func:`torchaudio.save`.
+
+In recent releases, more powerful IO features were added in :py:mod:`torchaudio.io`.
+These features are based on FFmpeg libraries, thus cross-platform and can handle
+wide variety of media formats, including audio and video, coming from many different source.
+
+
+.. toctree::
+   :maxdepth: 1
+   :caption: Media IO Tutorials
+
+   tutorials/audio_io_tutorial
+   tutorials/streamreader_basic_tutorial
+   tutorials/streamreader_advanced_tutorial
+   hw_acceleration_tutorial

examples/tutorials/streaming_api2_tutorial.py → examples/tutorials/streamreader_advanced_tutorial.py

 """
-Media Stream API - Pt. 2
-========================
+StreamReader Advanced Usages
+============================
 
 This tutorial is the continuation of
-`Media Stream API - Pt.1 <./streaming_api_tutorial.html>`__.
+`StreamReader Basic Usages <./streaming_api_tutorial.html>`__.
 
-This shows how to use `StreamReader` for
+This shows how to use :py:class:`~torchaudio.io.StreamReader` for
 
 - Device inputs, such as microphone, webcam and screen recording
 - Generating synthetic audio / video

examples/tutorials/streaming_api_tutorial.py → examples/tutorials/streamreader_basic_tutorial.py

 """
-Media Stream API - Pt. 1
-========================
+StreamReader Basic Usages
+=========================
 
-This tutorial shows how to use torchaudio's I/O stream API to
+This tutorial shows how to use :py:class:`torchaudio.io.StreamReader` to
 fetch and decode audio/video data and apply preprocessings that
 libavfilter provides.