Update UniTask README Example

Assets/YooAsset/Samples~/UniTask Sample/README.md

@@ -8,13 +8,16 @@
 ## 代码示例
 
 ```csharp
+public async UniTask Example(IProgress<float> progress = null, PlayerLoopTiming timing = PlayerLoopTiming.Update)
+{
     var handle = YooAssets.LoadAssetAsync<GameObject>("Assets/Res/Prefabs/  TestImg.prefab");
 
-await handle.ToUniTask();
+    await handle.ToUniTask(progress, timing);
 
     var obj = handle.AssetObject as GameObject;
     var go  = Instantiate(obj, transform);
 
     go.transform.localPosition = Vector3.zero;
     go.transform.localScale    = Vector3.one;
+}
 ```