message: Add link to migration guide in README.md
diff: @@ -30,7 +30,7 @@ npm i material-ui-pickers
  yarn add material-ui-pickers
  ```
  -Next channel (v3-alpha). [Docs site](https://next.material-ui-pickers.dev/).
  +Next channel (v3-alpha). [Docs site](https://next.material-ui-pickers.dev/). [Migration guide](https://next.material-ui-pickers.dev/guides/upgrading-to-v3)
  ```sh
  // via npm
  