Add useExtensions option

js-packages/webpack-config/README.md

@@ -9,7 +9,32 @@ This package generates a [Webpack](https://webpack.js.org) config object that wi
 ```js
 var config = require('flarum-webpack-config');
 
-module.exports = config();
+module.exports = config(options);
 ```
 
 To merge in custom Webpack config options, use [webpack-merge](https://www.npmjs.com/package/webpack-merge).
+
+## Options
+
+### `useExtensions`
+
+`Array<string>`, defaults to `[]`.
+
+An array of extensions whose modules should be made available. This is a shortcut to add [`externals`](https://webpack.js.org/configuration/externals/) configuration for extension modules. Imported extension modules will not be bundled, but will instead refer to the extension's exports included in the Flarum runtime (ie. `flarum.extensions["vendor/package"]`).
+
+For example, to access the Tags extension module within your extension:
+
+**forum.js**
+
+```js
+import { Tag } from '@flarum/flarum-ext-tags/forum';
+```
+
+**webpack.config.js**
+
+```js
+module.exports = config({
+  useExtensions: ['flarum/flarum-ext-tags']
+});
+```
+