[PYTHON] Api doc python with multiple authentications (#928)

* [PYTHON] better code snippet for API usage with authentication

* update python samples

samples/client/petstore/python-asyncio/docs/StoreApi.md

@@ -65,6 +65,8 @@ Returns pet inventories by status
 Returns a map of status codes to quantities
 
 ### Example
+
+* Api Key Authentication (api_key): 
 ```python
 from __future__ import print_function
 import time