Update MIGRATION.md, re: webpack 5

- This area was a point of confusion
- Attempted to reduce confusion while maintaining existing headings (so that anchor links already shared don't break)

MIGRATION.md

@@ -11,7 +11,10 @@
   - [Loader behavior with args changes](#loader-behavior-with-args-changes)
   - [Angular component parameter removed](#angular-component-parameter-removed)
 - [From version 6.2.x to 6.3.0](#from-version-62x-to-630)
-  - [Webpack 5 manager build](#webpack-5-manager-build)
+  - [Webpack 5](#webpack-5-manager-build)
+    - [Fixing hoisting issues](#fixing-hoisting-issues)
+      - [Webpack 5 manager build](#webpack-5-manager-build)
+      - [Wrong webpack version](#wrong-webpack-version)
   - [Angular 12 upgrade](#angular-12-upgrade)
   - [Lit support](#lit-support)
   - [No longer inferring default values of args](#no-longer-inferring-default-values-of-args)
@@ -333,29 +336,9 @@ export const MyStory = () => ({ component: MyComponent, ... })
 
 ## From version 6.2.x to 6.3.0
 
-### Webpack 5 manager build
+### Webpack 5
 
-Storybook 6.2 introduced **experimental** webpack5 support for building user components. Storybook 6.3 also supports building the manager UI in webpack 5 to avoid strange hoisting issues.
-
-If you're upgrading from 6.2 and already using the experimental webpack5 feature, this might be a breaking change (hence the 'experimental' label) and you should try adding the manager builder:
-
-```shell
-yarn add @storybook/manager-webpack5 --dev
-# Or
-npm install @storybook/manager-webpack5 --save-dev
-```
-
-Because Storybook uses `webpack@4` as the default, it's possible for the wrong version of webpack to get hoisted by your package manager. If you receive an error that looks like you might be using the wrong version of webpack, install `webpack@5` explicitly as a dev dependency to force it to be hoisted:
-
-```shell
-yarn add webpack@5 --dev
-# Or
-npm install webpack@5 --save-dev
-```
-
-### Angular 12 upgrade
-
-Storybook 6.3 supports Angular 12 out of the box when you install it fresh. However, if you're upgrading your project from a previous version, you'll need to do the following steps to force Storybook to use webpack 5 for building your project:
+Storybook 6.3 brings opt-in support for building both your project and the manager UI with webpack 5. To do so:
 
 ```shell
 yarn add @storybook/builder-webpack5@next @storybook/manager-webpack5 --dev
@@ -373,6 +356,34 @@ module.exports = {
 };
 ```
 
+#### Fixing hoisting issues
+
+##### Webpack 5 manager build
+
+Storybook 6.2 introduced **experimental** webpack5 support for building user components. Storybook 6.3 also supports building the manager UI in webpack 5 to avoid strange hoisting issues.
+
+If you're upgrading from 6.2 and already using the experimental webpack5 feature, this might be a breaking change (hence the 'experimental' label) and you should try adding the manager builder:
+
+```shell
+yarn add @storybook/manager-webpack5 --dev
+# Or
+npm install @storybook/manager-webpack5 --save-dev
+```
+
+##### Wrong webpack version
+
+Because Storybook uses `webpack@4` as the default, it's possible for the wrong version of webpack to get hoisted by your package manager. If you receive an error that looks like you might be using the wrong version of webpack, install `webpack@5` explicitly as a dev dependency to force it to be hoisted:
+
+```shell
+yarn add webpack@5 --dev
+# Or
+npm install webpack@5 --save-dev
+```
+
+### Angular 12 upgrade
+
+Storybook 6.3 supports Angular 12 out of the box when you install it fresh. However, if you're upgrading your project from a previous version, you'll need to [follow the steps for opting-in to webpack 5](#webpack-5).
+
 ### Lit support
 
 Storybook 6.3 introduces Lit 2 support in a non-breaking way to ease migration from `lit-html`/`lit-element` to `lit`.