improve migration doc

website/docs/migrating-from-v1-to-v2.md

@@ -609,6 +609,8 @@ You might want to refer to our migration PRs for [Create React App](https://gith
 
 For any questions, you can ask in the [`#docusaurus-1-to-2-migration` Discord channel](https://discordapp.com/invite/kYaNd6V). Feel free to tag [@yangshun](https://github.com/yangshun) in any migration PRs if you would like us to have a look.
 
+---
+
 ## Versioned Site
 
 :::caution
@@ -617,8 +619,6 @@ The versioning feature is a work in progress! Although we've implemented docs ve
 
 :::
 
-## Changes from v1
-
 Read up https://v2.docusaurus.io/blog/2018/09/11/Towards-Docusaurus-2#versioning first for problems in v1's approach.
 
 ### Migrate your `versioned_docs` front matter