Update CRA guide

Create React App is the most looked at resource by users here on GitHub.
But it’s suggesting an old, unmaintained, and buggy way to use MDX.

This instead updates the guide to use our maintained projects, without
having to eject from CRA.

As CRA itself is an ever-changing “init” tool, which can support MDX by
following a couple steps, I don’t think it’s wise to have an example in
the project: we want folks to do `npx create-react-app ...`, not clone
our custom example.

Not having CRA checked in also makes for a faster `yarn install`.

Perhaps developing our own [CRA
template](https://create-react-app.dev/docs/custom-templates) might be
nice for the future, but for now I’ve kept it at an up to date and
working guide.

Related to GH-1015.
Related to GH-1388.

Closes GH-365.
Closes GH-589.

Author: wooorm

.gitignore

@@ -11,7 +11,6 @@ bundle.js
 tmp
 artifacts
 .*cache
-public
 .npmrc
 .nyc_output/
 coverage/

docs/getting-started/create-react-app.mdx

@@ -1,50 +1,92 @@
 # Create React App
 
-Please note there’s a [known bug][] with
-the macro so live reloading doesn’t
-currently work.
-
-With Create React App you will need to use
-[`mdx.macro`][mdx-macro].
+First, create a new app with [CRA][] and change directory to enter it:
 
 ```sh
 npx create-react-app my-app
-yarn add mdx.macro
+cd my-app
+```
+
+Second, we need to configure some build tools.
+Install [`@mdx-js/loader`][loader] and [`babel-loader`][babel-loader] as dev
+dependencies:
+
+```sh
+yarn add @mdx-js/loader babel-loader --dev
+```
+
+Also make sure that JSX in MDX is handled by Babel by creating a `.babelrc` JSON
+file in the project root of `my-app`:
+
+```json
+{
+  "presets": ["@babel/preset-react"]
+}
+```
+
+Third, we can add our MDX content.
+Create an MDX file `Content.mdx` in the `src/` folder:
+
+```mdx
+export const Box = () => (
+  <div style={{padding: 20, backgroundColor: 'tomato'}} />
+)
+
+# Hello, world!
+
+This is **markdown** with <span style={{color: "red"}}>JSX</span>: MDX!
+
+<Box />
 ```
 
-Then create the following `src/App.js`:
+And to use that MDX content in the app, replace the contents of `App.js` in the
+`src/` folder with:
 
 ```js
-// src/App.js
-
-import React, {lazy, Component, Suspense} from 'react'
-import {importMDX} from 'mdx.macro'
-
-const Content = lazy(() => importMDX('./Content.mdx'))
-
-class App extends Component {
-  render() {
-    return (
-      <div>
-        <Suspense fallback={<div>Loading...</div>}>
-          <Content />
-        </Suspense>
-      </div>
-    )
-  }
+/* eslint-disable import/no-webpack-loader-syntax */
+import Content from '!babel-loader!@mdx-js/loader!./Content.mdx'
+
+function App() {
+  return <Content />
 }
 
 export default App
 ```
 
-And then create the following `src/Content.mdx`:
+We’re almost done!
+To start the development server, run:
 
-```md
-# Hello, world!
+```sh
+yarn start
 ```
 
-[See the full example][cra-example]
+**…but you will probably get this error**:
+
+```txt
+$ react-scripts start
+
+There might be a problem with the project dependency tree.
+It is likely not a bug in Create React App, but something you need to fix locally.
+
+The react-scripts package provided by Create React App requires a dependency:
+
+  "babel-loader": "$VERSION"
+…
+```
+
+CRA expects a certain `babel-loader` version but MDX also needs one.
+To fix the error, make sure the two `babel-loader` versions match, by running
+the following:
+
+```sh
+yarn add babel-loader@$VERSION --dev
+```
+
+(where `$VERSION` is the version number printed in the error message, such as
+`8.1.0`).
+
+Then, running `yarn start` again should do the trick! ✨
 
-[mdx-macro]: https://www.npmjs.com/package/mdx.macro
-[cra-example]: https://github.com/mdx-js/mdx/tree/master/examples/create-react-app
-[known bug]: https://github.com/facebook/create-react-app/issues/5580
+[cra]: https://github.com/facebook/create-react-app
+[loader]: https://github.com/mdx-js/mdx/tree/main/packages/loader
+[babel-loader]: https://webpack.js.org/loaders/babel-loader/

docs/getting-started/index.mdx

@@ -411,7 +411,6 @@ playing around you can use `npm init`:
 - `npm init mdx` [`webpack`](/getting-started/webpack)
 - `npm init mdx` [`parcel`](/getting-started/parcel)
 - `npm init mdx` [`next`](/getting-started/next)
-- `npm init mdx` [`create-react-app`](/getting-started/create-react-app)
 - `npm init mdx` [`gatsby`](/getting-started/gatsby)
 - `npm init mdx` [`react-static`](/getting-started/react-static)