Added MIGRATION instructions for Angular 13 / SB6.4 for Angular

MIGRATION.md

@@ -17,7 +17,10 @@
   - [Emotion11 quasi-compatibility](#emotion11-quasi-compatibility)
   - [Babel mode v7](#babel-mode-v7)
   - [Loader behavior with args changes](#loader-behavior-with-args-changes)
-  - [Angular component parameter removed](#angular-component-parameter-removed)
+  - [6.4 Angular changes](#64-angular-changes)
+    - [SB Angular builder](#sb-angular-builder)
+    - [Angular13](#angular13)
+    - [Angular component parameter removed](#angular-component-parameter-removed)
   - [6.4 deprecations](#64-deprecations)
     - [Deprecated --static-dir CLI flag](#deprecated---static-dir-cli-flag)
 - [From version 6.2.x to 6.3.0](#from-version-62x-to-630)
@@ -470,7 +473,53 @@ This will create a `.babelrc.json` file. This file includes a bunch of babel plu
 
 In 6.4 the behavior of loaders when arg changes occurred was tweaked so loaders do not re-run. Instead the previous value of the loader is passed to the story, irrespective of the new args.
 
-### Angular component parameter removed
+### 6.4 Angular changes
+
+#### SB Angular builder
+
+Since SB6.3, Storybook for Angular supports a builder configuration in your project's `angular.json`. This provides an Angular-style configuration for running and building your Storybook. The full builder documentation will be shown in the [main documentation page](https://storybook.js.org/docs/angular) soon, but for now you can check out an example here:
+
+- `start-storybook`: https://github.com/storybookjs/storybook/blob/next/examples/angular-cli/angular.json#L78
+- `build-storybook`: https://github.com/storybookjs/storybook/blob/next/examples/angular-cli/angular.json#L86
+
+#### Angular13
+
+Angular 13 introduces breaking changes that require updating your Storybook configuration if you are migrating from a previous version of Angular.
+
+Most notably, the documented way of including global styles is no longer supported by Angular13. Previously you could write the following in your `.storybook/preview.js` config:
+
+```
+import '!style-loader!css-loader!sass-loader!./styles.scss';
+```
+
+If you use Angular 13 and above, you should use the builder configuration instead:
+
+```json
+   "my-default-project": {
+      "architect": {
+        "build": {
+          "builder": "@angular-devkit/build-angular:browser",
+          "options": {
+            "styles": ["src/styles.css", "src/styles.scss"],
+          }
+        }
+      },
+   },
+```
+
+If you need storybook-specific styles separate from your app, you can configure the styles in the [SB Angular builder](#sb-angular-builder), which completely overrides your project's styles:
+
+```json
+      "storybook": {
+        "builder": "@storybook/angular:start-storybook",
+        "options": {
+          "browserTarget": "my-default-project:build",
+          "styles": [".storybook/custom-styles.scss"],
+        },
+      }
+```
+
+#### Angular component parameter removed
 
 In SB6.3 and earlier, the `default.component` metadata was implemented as a parameter, meaning that stories could set `parameters.component` to override the default export. This was an internal implementation that was never documented, but it was mistakenly used in some Angular examples.