fix drive token generation and update readme

[shubhindia]

Signed-off-by: Shubham Gopale [email protected]

[UsamaKarim]

Still error

Traceback (most recent call last):
  File "/Users/amigo/dev/mirror-bot/generate_drive_token.py", line 18, in <module>
    credentials.refresh(Request())
  File "/opt/homebrew/lib/python3.9/site-packages/google/oauth2/credentials.py", line 302, in refresh
    ) = reauth.refresh_grant(
  File "/opt/homebrew/lib/python3.9/site-packages/google/oauth2/reauth.py", line 347, in refresh_grant
    _client._handle_error_response(response_data)
  File "/opt/homebrew/lib/python3.9/site-packages/google/oauth2/_client.py", line 60, in _handle_error_response
    raise exceptions.RefreshError(error_details, response_data)
google.auth.exceptions.RefreshError: ('invalid_grant: Token has been expired or revoked.', {

[shubhindia]

@UsamaKarim error says token might be expired or revoked. Please create a new credentials or download the refreshed ones from your gcloud console.