chore: update README (Vue 3.0) (#20345)

add migration guide to Vue 3.0

README.md

@@ -36,6 +36,12 @@
   </a>
 </p>
 
+> A Vue.js 2.0 UI Toolkit for Web.
+
+Element will stay with Vue 2.x 
+
+For Vue 3.0, we recommend using [Element Plus](https://github.com/element-plus/element-plus) from the same team
+
 <p align="center">
   <b>Special thanks to the generous sponsorship by:</b>
 </p>
@@ -61,8 +67,6 @@
   </tbody>
 </table>
 
-> A Vue.js 2.0 UI Toolkit for Web.
-
 ## Links
 - Homepage and documentation
   - [International users](http://element.eleme.io/#/en-US)