Add note about webpack 4. See #7

README.md

@@ -79,6 +79,8 @@ const cssLifecycles = singleSpaCss({
 
 ## Webpack Plugin
 
+**This plugin currently only supports webpack 5. See [issue 7](https://github.com/single-spa/single-spa-css/issues/7) to track webpack 4 support.**
+
 single-spa-css exposes a webpack plugin that integrates with [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) to allow you to load CSS files that are extracted and otherwise would not be loaded. The webpack plugin exposes the names of the extracted CSS files to your bundle under the `__webpack_require__.cssAssets` and `__webpack_require__.cssAssetFileName` variables. The `cssAssets` variable contains the name of the webpack chunk, and the `cssAssetFileName` function converts the chunk name into the extracted CSS asset's file name. These can be used manually, or you can specify the `webpackExtractedCss` option in single-spa-css to have it automatically mount and unmount those CSS files.
 
 ### Usage