Update README for the gRPC interceptors (#100)

Author: liyanhui1228

README.rst

@@ -253,6 +253,24 @@ setting in ``settings.py``:
         'ZIPKIN_EXPORTER_PORT': 9411,
     }
 
+gRPC Integration
+----------------
+
+OpenCensus provides the implementation of interceptors for both the client side
+and server side to instrument the gRPC requests and responses. The client
+interceptors are used to create a decorated channel that intercepts client
+gRPC calls and server interceptors act as decorators over handlers.
+
+gRPC interceptor is a new feature in the grpcio1.8.0 release, please upgrade
+your grpcio to the latest version to use this feature.
+
+For sample usage, please refer to the hello world example in the examples
+directory.
+
+More information about the gRPC interceptors please see the `proposal`_.
+
+.. _proposal: https://github.com/mehrdada/proposal/blob/python-interceptors/L13-Python-Interceptors.md
+
 Service Integration
 -------------------