Checkpoint for gRPC implementation

examples/hello_world/proto/hello.proto

@@ -0,0 +1,15 @@
+syntax = "proto3";
+
+package hello;
+
+service HelloWorldService {
+  rpc HelloWorld (HelloRequest) returns (HelloResponse);
+}
+
+message HelloRequest {
+  string name = 1;
+}
+
+message HelloResponse {
+  string message = 1;
+}