Update documentation for Storybook v7

[rtivital]

It is now required to use new addons api in Storybook v7 – https://storybook.js.org/docs/react/addons/addons-api#addonsgetchannel

The events code won't work with Storybook 7.x:

import addons from '@storybook/addons';
import { addDecorator } from '@storybook/react';
import { DARK_MODE_EVENT_NAME } from 'storybook-dark-mode';

// your theme provider
import ThemeContext from './theme';

// get channel to listen to event emitter
const channel = addons.getChannel();

// create a component that listens for the DARK_MODE event
function ThemeWrapper(props) {
  // this example uses hook but you can also use class component as well
  const [isDark, setDark] = useState(false);

  useEffect(() => {
    // listen to DARK_MODE event
    channel.on(DARK_MODE_EVENT_NAME, setDark);
    return () => channel.off(DARK_MODE_EVENT_NAME, setDark);
  }, [channel, setDark]);

  // render your custom theme provider
  return (
    <ThemeContext.Provider value={isDark ? darkTheme : defaultTheme}>
      {props.children}
    </ThemeContext.Provider>
  );
}

export const decorators = [renderStory => <ThemeWrapper>{renderStory()}</ThemeWrapper>)]

It should be changed to:

import { useEffect } from 'react';
import { addons } from "@storybook/preview-api";
import { DARK_MODE_EVENT_NAME } from 'storybook-dark-mode';

// your theme provider
import ThemeContext from './theme';

// get channel to listen to event emitter
const channel = addons.getChannel();

// create a component that listens for the DARK_MODE event
function ThemeWrapper(props) {
  // this example uses hook but you can also use class component as well
  const [isDark, setDark] = useState(false);

  useEffect(() => {
    // listen to DARK_MODE event
    channel.on(DARK_MODE_EVENT_NAME, setDark);
    return () => channel.off(DARK_MODE_EVENT_NAME, setDark);
  }, [channel, setDark]);

  // render your custom theme provider
  return (
    <ThemeContext.Provider value={isDark ? darkTheme : defaultTheme}>
      {props.children}
    </ThemeContext.Provider>
  );
}

export const decorators = [renderStory => <ThemeWrapper>{renderStory()}</ThemeWrapper>)]

I've tested it to work correctly with Storybook 7.0.17. If you are interested, I can send a PR with a fix.

[hipstersmoothie]

If you want to submit a pr to update the docs I'll merge!