Flatbuffers library added to the list of third party libraries.

third_party/flatbuffers/docs/source/gRPC/CppUsage.md

@@ -0,0 +1,29 @@
+Use in C++    {#flatbuffers_grpc_guide_use_cpp}
+==========
+
+## Before you get started
+
+Before diving into the FlatBuffers gRPC usage in C++, you should already be
+familiar with the following:
+
+- FlatBuffers as a serialization format
+- [gRPC](http://www.grpc.io/docs/) usage
+
+## Using the FlatBuffers gRPC C++ library
+
+NOTE: The examples below are also in the `grpc/samples/greeter` directory.
+
+We will illustrate usage with the following schema:
+
+@include grpc/samples/greeter/greeter.fbs
+
+When we run `flatc`, we pass in the `--grpc` option and generage an additional
+`greeter.grpc.fb.h` and `greeter.grpc.fb.cc`.
+
+Example server code looks like this:
+
+@include grpc/samples/greeter/server.cpp
+
+Example client code looks like this:
+
+@include grpc/samples/greeter/client.cpp