doc: update initialization with sap-client example

Author: ksaito1125

docs/usage/initialization.rst

@@ -21,6 +21,23 @@ Basic initialization which is going to work for everybody:
 
     northwind = pyodata.Client(SERVICE_URL, requests.Session())
 
+Get the service proxy client for an OData service requiring sap-client parameter
+--------------------------------------------------------------------------------
+
+This is a sample when it is necessary to specify sap-client:
+
+.. code-block:: python
+
+    import pyodata
+    import requests
+
+    SERVICE_URL = 'http://services.odata.org/V2/Northwind/Northwind.svc/'
+
+    session = requests.Session()
+    param = {'sap-client': '510'}
+    session.params = param
+    northwind = pyodata.Client(SERVICE_URL, session)
+
 Get the service proxy client for an OData service requiring authentication
 --------------------------------------------------------------------------