Fix #24 - Add information about minimization

Add a note and example about minimizing CSS output in Webpack 4.

Author: mike-marcacci

README.md

@@ -66,6 +66,36 @@ module.exports = {
 }
 ```
 
+### Minimizing For Production
+
+While Webpack 5 is likely to come with a CSS minimizer built-in, with Webpack 4 you need to bring your own. To minify your the output, use a plugin like optimize-css-assets-webpack-plugin](https://github.com/NMFR/optimize-css-assets-webpack-plugin):
+
+```js
+const MiniCssExtractPlugin = require("mini-css-extract-plugin");
+const OptimizeCSSAssetsPlugin = require("optimize-css-assets-webpack-plugin");
+module.exports = {
+  plugins: [
+    new MiniCssExtractPlugin({
+      filename: "[name].css",
+      chunkFilename: "[id].css"
+    }),
+    new OptimizeCssAssetsPlugin()
+  ],
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [
+          MiniCssExtractPlugin.loader,
+          "css-loader"
+        ]
+      }
+    ]
+  }
+}
+```
+
+
 <h2 align="center">Maintainers</h2>
 
 <table>