fix option in authentication

README.md

@@ -46,7 +46,7 @@ The package includes a default ```client_secrets.json``` file. If you plan to ma
 * Side menu: _APIs & auth_ -> _Credentials_.
 * _Create new Client ID_: Application type: _Installed application_ + _Other_
 * _Download JSON_: save the file to your local system. 
-* Use the saved JSON as your credentials file: ```--credentials-file=CREDENTIALS_FILE```
+* Use the saved JSON as your credentials file: ```--client-secrets=CLIENT_SECRETS```
 
 Examples
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