Update: examples/graceful-shutdown/server.go (#1530)

* Update server.go

It's necessary that  catching  ctx.Done()

* Update server.go

* Update server.go

* Update README.md

* Update README.md

README.md

@@ -1673,6 +1673,11 @@ func main() {
 	if err := srv.Shutdown(ctx); err != nil {
 		log.Fatal("Server Shutdown:", err)
 	}
+	// catching ctx.Done(). timeout of 5 seconds.
+	select {
+	case <-ctx.Done():
+		log.Println("timeout of 5 seconds.")
+	}
 	log.Println("Server exiting")
 }
 ```