matching instructions with completed code for client (#43)

Match instructions in README with new completed client code

Author: cjqzhao

codelabs/grpc-go-getting-started/README.md

@@ -304,9 +304,12 @@ the server to respond, and will either return a response or an error.
 Calling the simple RPC `GetFeature` is nearly as straightforward as calling a local method.
 
 ```go
-feature, err := client.GetFeature(context.Background(), &pb.Point{Latitude: 409146138, Longitude: -746188906})
+point := &pb.Point{Latitude: 409146138, Longitude: -746188906}
+log.Printf("Getting feature for point (%d, %d)", point.Latitude, point.Longitude)
+// Call GetFeature method on the client.
+feature, err := client.GetFeature(context.TODO(), point)
 if err != nil {
-    ...
+  log.Fatalf("client.GetFeature failed: %v", err)
 }
 ```