Update audio_preprocessing_tutorial.py (#1202)

Adds a comment for running this tutorial in Google Colab.

Author: brianjo

beginner_source/audio_preprocessing_tutorial.py

@@ -18,6 +18,8 @@
 
 """
 
+# Uncomment the following line to run in Google Colab
+# !pip install torchaudio 
 import torch
 import torchaudio
 import requests