code: function main() {
    var server = new grpc.Server();
    server.addService(hello_proto.Greeter.service, {sayHello: sayHello});
    server.bind('0.0.0.0:50051', grpc.ServerCredentials.createInsecure());
    server.start();
  }
docs: Starts an RPC server that receives requests for the Greeter service at the
  sample server port