Update doc regarding dropping Python3.6 support (#2139)

Summary:
Drop support for python 3.6, and update dependencies documentation. More details [Issue 2051](https://github.com/pytorch/audio/issues/2051).

Pull Request resolved: https://github.com/pytorch/audio/pull/2139

Reviewed By: mthrok

Differential Revision: D33454583

Pulled By: wernerchao

fbshipit-source-id: 64eccb38e26853ba63f72fb92723e3f0155e806e

README.md

@@ -33,7 +33,7 @@ The following are the corresponding ``torchaudio`` versions and supported Python
 
 | ``torch``                | ``torchaudio``           | ``python``                      |
 | ------------------------ | ------------------------ | ------------------------------- |
-| ``master`` / ``nightly`` | ``main`` / ``nightly``   | ``>=3.6``, ``<=3.9``            |
+| ``master`` / ``nightly`` | ``main`` / ``nightly``   | ``>=3.7``, ``<=3.9``            |
 | ``1.10.0``               | ``0.10.0``               | ``>=3.6``, ``<=3.9``            |
 | ``1.9.1``                | ``0.9.1``                | ``>=3.6``, ``<=3.9``            |
 | ``1.9.0``                | ``0.9.0``                | ``>=3.6``, ``<=3.9``            |

setup.py

@@ -159,7 +159,6 @@ def _main():
             "Operating System :: Microsoft :: Windows",
             "Operating System :: POSIX",
             "Programming Language :: C++",
-            "Programming Language :: Python :: 3.6",
             "Programming Language :: Python :: 3.7",
             "Programming Language :: Python :: 3.8",
             "Programming Language :: Python :: 3.9",