docs: move babel v7 section to webpack

MIGRATION.md

@@ -19,7 +19,6 @@
     - [Change of root html IDs](#change-of-root-html-ids)
     - [Stories glob matches MDX files](#stories-glob-matches-mdx-files)
     - [Add strict mode](#add-strict-mode)
-    - [Babel mode v7 exclusively](#babel-mode-v7-exclusively)
     - [Importing plain markdown files with `transcludeMarkdown` has changed](#importing-plain-markdown-files-with-transcludemarkdown-has-changed)
   - [7.0 Core changes](#70-core-changes)
     - [7.0 feature flags removed](#70-feature-flags-removed)
@@ -34,6 +33,7 @@
     - [Vite cache moved to node\_modules/.cache/.vite-storybook](#vite-cache-moved-to-node_modulescachevite-storybook)
   - [7.0 Webpack changes](#70-webpack-changes)
     - [Webpack4 support discontinued](#webpack4-support-discontinued)
+    - [Babel mode v7 exclusively](#babel-mode-v7-exclusively)
     - [Postcss removed](#postcss-removed)
     - [Removed DLL flags](#removed-dll-flags)
   - [7.0 Framework-specific changes](#70-framework-specific-changes)
@@ -761,20 +761,6 @@ Starting in 7.0, Storybook's build tools add [`"use strict"`](https://developer.
 
 If user code in `.storybook/preview.js` or stories relies on "sloppy" mode behavior, it will need to be updated. As a workaround, it is sometimes possible to move the sloppy mode code inside a script tag in `.storybook/preview-head.html`.
 
-#### Babel mode v7 exclusively
-
-_Has automigration_
-
-Storybook now uses [Babel mode v7](#babel-mode-v7) exclusively. In 6.x, Storybook provided its own babel settings out of the box. Now, Storybook's uses your project's babel settings (`.babelrc`, `babel.config.js`, etc.) instead.
-
-In the new mode, Storybook expects you to provide a configuration file. If you want a configuration file that's equivalent to the 6.x default, you can run the following command in your project directory:
-
-```sh
-npx sb@next babelrc
-```
-
-This will create a `.babelrc.json` file. This file includes a bunch of babel plugins, so you may need to add new package devDependencies accordingly.
-
 #### Importing plain markdown files with `transcludeMarkdown` has changed
 
 The `transcludeMarkdown` option in `addon-docs` have been removed, and the automatic handling of `.md` files in Vite projects have also been disabled.
@@ -899,6 +885,23 @@ To upgrade:
 
 During the 7.0 dev cycle we will be updating this section with useful resources as we run across them.
 
+#### Babel mode v7 exclusively
+
+_Has automigration_
+
+Storybook now uses [Babel mode v7](#babel-mode-v7) exclusively. In 6.x, Storybook provided its own babel settings out of the box. Now, Storybook's uses your project's babel settings (`.babelrc`, `babel.config.js`, etc.) instead.
+
+> Note:
+> If you are using @storybook/react-webpack5 with the @storybook/preset-create-react-app package, you don't need to do anything. The preset already provides the babel configuration you need.
+
+In the new mode, Storybook expects you to provide a configuration file. Depending on the complexity your project, Storybook will fail to run without a babel configuration. If you want a configuration file that's equivalent to the 6.x default, you can run the following command in your project directory:
+
+```sh
+npx storybook@next babelrc
+```
+
+This command will create a `.babelrc.json` file in your project, containing a few babel plugins which will be installed as dev dependencies.
+
 #### Postcss removed
 
 Storybook 6.x installed postcss by default. In 7.0 built-in support has been removed for Webpack-based frameworks. If you need it, you can add it back using [`@storybook/addon-postcss`](https://github.com/storybookjs/addon-postcss).