update readme

README.md

 A UIWidgets App is written in **C# Scripts**. Please follow the steps to create an App and play it
 in Unity Editor.
 
-1. Create a new C# Script named "ExampleCanvas.cs" and paste the following codes into it.
+1. Create a new C# Script named "UIWidgetsExample.cs" and paste the following codes into it.
+    using Unity.UIWidgets.animation;
     using Unity.UIWidgets.engine;
     using Unity.UIWidgets.foundation;
     using Unity.UIWidgets.material;
     namespace UIWidgetsSample {
-        public class ExampleCanvas : WidgetCanvas {
+        public class UIWidgetsExample : UIWidgetsPanel {
-                    
+    
-                
+    
-                
-            protected override Widget getWidget() {
-                return new ExampleApp();
+    
+            protected override Widget createWidget() {
+                return new WidgetsApp(
+                    home: new ExampleApp(),
+                    pageRouteBuilder: this.pageRouteBuilder);
+            }
+    
+            protected virtual PageRouteFactory pageRouteBuilder {
+                get {
+                    return (RouteSettings settings, WidgetBuilder builder) =>
+                        new PageRouteBuilder(
+                            settings: settings,
+                            pageBuilder: (BuildContext context, Animation<float> animation,
+                                Animation<float> secondaryAnimation) => builder(context)
+                        );
+                }
             }
     
             class ExampleApp : StatefulWidget {
                             new GestureDetector(
                                 onTap: () => {
                                     this.setState(()
-                                     => {
+                                        => {
                                         this.counter++;
                                     });
                                 },