message: Add section about Storybook to v4 migration guide
diff: - [New package names](#new-package-names)
  - [Better TypeScript support](#better-typescript-support)
  - [Typing the theme](#typing-the-theme)
  + - [Compatibility with Storybook](#compatibility-with-storybook)
  - [New brand icons](#new-brand-icons)
  - [Overview of `@sumup/icons` v2](#overview-of-sumupicons-v2)
  - [Migrating to `@sumup/icons` v2](#migrating-to-sumupicons-v2)
  @@ -162,6 +163,32 @@ const RedCard = styled(Card)(
  );
  ```
  +#### Compatibility with Storybook
  +
  +In case you're using [Storybook](https://storybook.js.org/) in your application, you'll need to tweak the Storybook Webpack config to make it compatible with Emotion 11 (Storybook is still on Emotion 10).
  +
  +Make sure that references to Emotion packages inside Storybook are pointing to the v11 packages:
  +
  +```js
  +// .storybook/main.js
  +
  +const path = require('path');
  +const toPath = (_path) => path.join(process.cwd(), _path);
  +
  +module.exports = {
  + webpackFinal: async (config) => {
  + // Add compatibility with Emotion 11
  + config.resolve.alias = {
  + ...config.resolve.alias,
  + '@emotion/core': toPath('node_modules/@emotion/react'),
  + '@emotion/styled': toPath('node_modules/@emotion/styled'),
  + 'emotion-theming': toPath('node_modules/@emotion/react'),
  + };
  + return config;
  + },
  +};
  +```
  +
  ### New brand icons
  Circuit v4 ships with the [new brand icons](https://circuit.sumup.com/?path=/story/features-icons--page) from `@sumup/icons` v2.
  