refine readme

add preview tag
add Runtime Environment

README-ZH.md

-# UIWidgets
+# UIWidgets 2.0 （preview）
 
 
 ## 介绍
 UIWidgets主要来自[Flutter](https://github.com/flutter/flutter)。但UIWidgets通过使用强大的Unity引擎为开发人员提供了许多新功能，显著地改进他们开发的应用性能和工作流程。
+
+UIWidgets 2.0是UIWidgets的最新版本，它主要着力于UI绘制相关的整体性能优化。经测试，UIWidgets 2.0在iPhone 6等部分机型上的帧率相对1.0版本可以取得10%左右的提升。如果因为各种原因您还需要使用UIWidgets 1.0，请在Releases中下载对应的包或者使用uiwidgets_1.0分支。
 
 #### 效率
 通过使用最新的Unity渲染SDK，UIWidgets应用可以非常快速地运行并且大多数时间保持大于60fps的速度。
    ```
 在unity的PackageManager中，选择添加添加local file。选中```/com.unity.uiwidgets```下的```package.json```。
 
-对于windows,请用在```com.unity.uiwidgets/Runtime/Plugins/x86_64```下的 ```libEGL.dll, libGLESv2.dll```替换编辑器中中相应文件
+对于windows,请用在```com.unity.uiwidgets/Runtime/Plugins/x86_64```下的 ```libEGL.dll, libGLESv2.dll```替换编辑器中相应文件
+
+#### 运行环境
+
+UIWidgets目前暂时只支持MacOS（Metal），iOS（Metal），Android（Armv7，OpenGLes）以及 Windows（Direct3D11）。我们后续会针对更广泛的运行环境进行适配，敬请期待。
 
 ## 入门指南
 

README.md

-# UIWidgets
+# UIWidgets 2.0 (preview)
 [中文](README-ZH.md)
 
 
 UIWidgets is mainly derived from [Flutter](https://github.com/flutter/flutter). However, taking advantage of
 the powerful Unity Engine, it offers developers many new features to improve their Apps
 as well as the develop workflow significantly.
+
+As the latest version, UIWidgets 2.0 aims to optmize the overall performance of the package. Specifically, a performance gain around 10% is observed on  mobile devices like iPhone 6 after upgrading to UIWidgets 2.0. However, if you still want to use the original UIWidgets 1.0, please download the archived packages from Releases or switch your working branch to uiwidgets_1.0.
 
 #### Efficiency
 Using the latest Unity rendering SDKs, a UIWidgets App can run very fast and keep >60fps in most times.
 In PackageManger of unity, select add local file. select ```package.json``` under ```/com.unity.uiwidgets```
 
 for windows, please replace ```libEGL.dll, libGLESv2.dll``` in Editor from ones in ```com.unity.uiwidgets/Runtime/Plugins/x86_64``
+
+#### Runtime Environment
+
+Currently UIWidgets only support MacOS(Metal), iOS(Metal), Android(Armv7, OpenGLes) and Windows(Direct3D11). More devices will be supported in the future.
 
 ## Getting Start