Also updating inline comments for the secret param

Author: rayluo

sample/authorization-code-flow-sample/authorization_code_flow_sample.py

@@ -13,8 +13,10 @@
 }
 
 You can then run this sample with a JSON configuration file:
-    python sample.py parameters.json
-    On the browser open http://localhost:5000/
+
+    python sample.py parameters.json your_flask_session_secret_here
+
+And the on the browser open http://localhost:5000/
 
 """