4.1 migration WIP

MIGRATION.md

@@ -1,5 +1,8 @@
 # Migration
 
+- [From version 4.0.x to 4.1.x](#from-version-40x-to-41x)
+  - [Private addon config](#private-addon-config)
+  - [React 15.x](#react-15x)
 - [From version 3.4.x to 4.0.x](#from-version-34x-to-40x)
   - [React 16.3+](#react-163)
   - [Generic addons](#generic-addons)
@@ -34,9 +37,21 @@
   - [Packages renaming](#packages-renaming)
   - [Deprecated embedded addons](#deprecated-embedded-addons)
 
+## From version 4.0.x to 4.1.x
+
+There are are a few migrations you should be aware of in 4.1, including one unintentionally breaking change for advanced addon usage.
+
+## Private addon config
+
+If your Storybook contains custom addons defined that are defined in your app (as opposed to installed from packages) and those addons rely on reconfiguring webpack/babel, Storybook 4.1 may break for you. There's a workaround [described in the issue](https://github.com/storybooks/storybook/issues/4995), and we're working on official support in the next minor release.
+
+## React 15.x
+
+Storybook 4.1 supports React 15.x (which had been [lost in the 4.0 release](#react-163)). So if you've been blocked on upgrading, we've got you. You should be able to upgrade according to the 4.0 migration notes below, or following the [4.0 upgrade guide](https://medium.com/storybookjs/migrating-to-storybook-4-c65b19a03d2c).
+
 ## From version 3.4.x to 4.0.x
 
-With 4.0 as our first major release in over a year, we've collected a lot of cleanup tasks. Most of the deprecations have been marked for months, so we hope that there will be no significant impact on your project.
+With 4.0 as our first major release in over a year, we've collected a lot of cleanup tasks. Most of the deprecations have been marked for months, so we hope that there will be no significant impact on your project. We've also created a [step-by-step guide to help you upgrade](https://medium.com/storybookjs/migrating-to-storybook-4-c65b19a03d2c).
 
 ### React 16.3+
 
@@ -69,13 +84,13 @@ core.browser.esm.js:15 Uncaught TypeError: Object(...) is not a function
 4.x introduces generic addon decorators that are not tied to specific view layers [#3555](https://github.com/storybooks/storybook/pull/3555). So for example:
 
 ```js
-import { number } from "@storybook/addon-knobs/react";
+import { number } from '@storybook/addon-knobs/react';
 ```
 
 Becomes:
 
 ```js
-import { number } from "@storybook/addon-knobs";
+import { number } from '@storybook/addon-knobs';
 ```
 
 ### Knobs select ordering
@@ -245,7 +260,7 @@ Knobs users: there was a bug in 3.2.x where using the knobs addon imported all f
 In the case of React or React-Native, import knobs like this:
 
 ```js
-import { withKnobs, text, boolean, number } from "@storybook/addon-knobs/react";
+import { withKnobs, text, boolean, number } from '@storybook/addon-knobs/react';
 ```
 
 In the case of Vue: `import { ... } from '@storybook/addon-knobs/vue';`
@@ -273,10 +288,10 @@ We're in the process of upgrading our addons APIs. As a first step, we've upgrad
 Here's an example of using Notes and Info in 3.2 with the new API.
 
 ```js
-storiesOf("composition", module).add(
-  "new addons api",
-  withInfo("see Notes panel for composition info")(
-    withNotes({ text: "Composition: Info(Notes())" })(context => (
+storiesOf('composition', module).add(
+  'new addons api',
+  withInfo('see Notes panel for composition info')(
+    withNotes({ text: 'Composition: Info(Notes())' })(context => (
       <MyComponent name={context.story} />
     ))
   )
@@ -387,13 +402,13 @@ If you **are** using these addons, migrating is simple:
 - update your code:
   change `addons.js` like so:
   ```js
-  import "@storybook/addon-actions/register";
-  import "@storybook/addon-links/register";
+  import '@storybook/addon-actions/register';
+  import '@storybook/addon-links/register';
   ```
   change `x.story.js` like so:
   ```js
-  import React from "react";
-  import { storiesOf } from "@storybook/react";
-  import { action } from "@storybook/addon-actions";
-  import { linkTo } from "@storybook/addon-links";
+  import React from 'react';
+  import { storiesOf } from '@storybook/react';
+  import { action } from '@storybook/addon-actions';
+  import { linkTo } from '@storybook/addon-links';
   ```