doc: use a more friendly link to codemod tool (#3266)

Author: HerringtonDarkholme

website/docs/migration-guides/yew/from-0_20_0-to-next.mdx

@@ -12,7 +12,7 @@ import TabItem from '@theme/TabItem'
 
 ### Automated refactor
 
-With the help of https://crates.io/crates/ast-grep
+With the help of [https://ast-grep.github.io](https://ast-grep.github.io/guide/quick-start.html)
 Here are commands that can do the refactoring for you.
 
 ```bash