fix readme: update discussion site

README-ZH.md

 #### Wiki
 
 目前开发团队仍在改进UIWidgets Wiki。 由于UIWidgets主要来源于Flutter，你也可以参考Flutter Wiki中与UIWidgets API对应部分的详细描述。
-同时，你可以加入我们的讨论组( https://connect.unity.com/g/uiwidgets )。
+同时，你可以加入我们的讨论组( https://learn.unity.com/g/uiwidgets )。
 
 #### 常问问题解答
 

README.md

 The develop team is still working on the UIWidgets Wiki. However, since UIWidgets is mainly derived from Flutter,
  you can refer to Flutter Wiki to access detailed descriptions of UIWidgets APIs
  from those of their Flutter counterparts.
-Meanwhile, you can join the discussion channel at (https://connect.unity.com/g/uiwidgets)
+Meanwhile, you can join the discussion channel at (https://learn.unity.com/g/uiwidgets)
 
 #### FAQ