oauth2client should be listed as a requirement for Google Cloud Speech

[Qub3k]

Steps to reproduce

1. I followed the guide describing how to install dependencies necessary to make recognizer_instance.recognize_google_cloud work.
2. After issuing pip install google-cloud-speech I was expecting that recognizer_instance.recognize_google_cloud would work.
3. However, the only message I got was as follows: Could not request results from Google Cloud Speech service; missing google-api-python-client module: ensure that google-api-python-client is set up correctly..
4. (I use the code from the audio_transcribe.py example.)

Expected behaviour

I was expecting that satisfying the google-cloud-speech dependency would make recognizer_instance.recognize_google_cloud work.

Actual behaviour

The code returned the following error message: Could not request results from Google Cloud Speech service; missing google-api-python-client module: ensure that google-api-python-client is set up correctly..

I was expecting the code would point me in the direction of the oauth2client package (which was the actual root cause of the problem).

Is it possible to add the oauth2client package to the README.rst file in the section regarding dependencies for the recognizer_instance.recognize_google_cloud?

System information

My system is macOS Catalina 10.15.7 (19H114).

My Python version is 3.7.

My Pip version is 20.2.2.

My SpeechRecognition library version is 3.8.1.