docs: Updates file name suggestion in babel.md (#31198)

Author: FlxSaenger

docs/docs/how-to/custom-configuration/babel.md

@@ -14,7 +14,7 @@ If you only target newer browsers, see the [Browser Support](/docs/how-to/custom
 
 ## How to use a custom `.babelrc` file
 
-Gatsby ships with a default `.babelrc` setup that should work for most sites. If you'd like to add custom Babel presets or plugins, you can create your own `.babelrc` at the root of your site, import [`babel-preset-gatsby`](https://github.com/gatsbyjs/gatsby/tree/master/packages/babel-preset-gatsby), and add additional plugins, presets, and pass options to `babel-preset-gatsby`, e.g. `targets`.
+Gatsby ships with a default `.babelrc` setup that should work for most sites. If you'd like to add custom Babel presets or plugins, you can create your own `.babelrc` at the root of your site, import [`babel-preset-gatsby`](https://github.com/gatsbyjs/gatsby/tree/master/packages/babel-preset-gatsby), and add additional plugins, presets, and pass options to `babel-preset-gatsby`, e.g. `targets`. In case of using a [monorepo](https://babeljs.io/docs/en/configuration), you may want to call this file `babel.config.json`.
 
 ```shell
 npm install --save-dev babel-preset-gatsby