Update config guide to include client context params usage (#3894)

* update config rst with client context params

docs/source/guide/configuration.rst

@@ -114,6 +114,31 @@ You can configure how Boto3 uses proxies by specifying the ``proxies_config`` op
 
 With the addition of the ``proxies_config`` option shown here, the proxy will use the specified certificate file for authentication when using the HTTPS proxy.
 
+Using client context parameters
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Some services have configuration settings that are specific to their clients. These settings are called client context parameters. Please refer to the ``Client Context Parameters`` section of a service client's documentation for a list of available parameters and information on how to use them.
+
+.. _configure_client_context:
+
+Configuring client context parameters
+'''''''''''''''''''''''''''''''''''''
+You can configure client context parameters by passing a dictionary of key-value pairs to the ``client_context_params`` parameter in your ``Config``. Invalid parameter values or parameters that are not modeled by the service will be ignored.
+
+.. code-block:: python
+
+    import boto3
+    from botocore.config import Config
+
+    my_config = Config(
+        region_name='us-east-2',
+        client_context_params={
+            'my_great_context_param': 'foo'
+        }
+    )
+
+    client = boto3.client('kinesis', config=my_config)
+
+Boto3 does not support setting ``client_context_params`` per request. Differing configurations will require creation of a new client.
 
 Using environment variables 
 ---------------------------