Update babel docs to mention you can use babel.config.js. (#23434)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [x] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.

## Documentation / Examples

- [x] Make sure the linting passes

docs/advanced-features/customizing-babel-config.md

@@ -13,7 +13,7 @@ description: Extend the babel preset added by Next.js with your own configs.
 
 Next.js includes the `next/babel` preset to your app, which includes everything needed to compile React applications and server-side code. But if you want to extend the default Babel configs, it's also possible.
 
-To start, you only need to define a `.babelrc` file at the top of your app. If such a file is found, it will be considered as the _source of truth_, and therefore it needs to define what Next.js needs as well, which is the `next/babel` preset.
+To start, you only need to define a `.babelrc` file (or `babel.config.js`) at the top of your app. If such a file is found, it will be considered as the _source of truth_, and therefore it needs to define what Next.js needs as well, which is the `next/babel` preset.
 
 Here's an example `.babelrc` file: