Merge pull request #13180 from storybookjs/docs/addon-backgrounds-61-migration

docs(MIGRATION): add preset information for addon-backgrounds in 6.1

MIGRATION.md

@@ -3,6 +3,7 @@
 - [From version 6.1.x to 6.2.0](#from-version-61x-to-620)
   - [New Angular renderer](#new-angular-renderer)
 - [From version 6.0.x to 6.1.0](#from-version-60x-to-610)
+  - [Addon-backgrounds preset](#addon-backgrounds-preset)
   - [Single story hoisting](#single-story-hoisting)
   - [React peer dependencies](#react-peer-dependencies)
   - [6.1 deprecations](#61-deprecations)
@@ -156,6 +157,27 @@ Please also file an issue if you need to opt out. We plan to remove the legacy r
 
 ## From version 6.0.x to 6.1.0
 
+### Addon-backgrounds preset
+
+In 6.1 we introduced an unintentional breaking change to `addon-backgrounds`.
+
+The addon uses decorators which are set up automatically by a preset. The required preset is ignored if you register the addon in `main.js` withe the the `/register` entry point. This used to be valid in `v6.0.x` and earlier:
+```js
+module.exports = {
+  stories: ['../**/*.stories.js'],
+  addons: ['@storybook/addon-backgrounds/register'],
+};
+```
+
+To fix it, just replace `@storybook/addon-backgrounds/register` with `@storybook/addon-backgrounds`:
+
+```js
+module.exports = {
+  stories: ['../**/*.stories.js'],
+  addons: ['@storybook/addon-backgrounds'],
+};
+```
+
 ### Single story hoisting
 
 Stories which have **no siblings** (i.e. the component has only one story) and which name **exactly matches** the component name will now be hoisted up to replace their parent component in the sidebar. This means you can have a hierarchy like this: