docs: add information about minimization (webpack-contrib#35)

Author: mike-marcacci

README.md

@@ -66,6 +66,47 @@ 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 the output, use a plugin like [optimize-css-assets-webpack-plugin](https://github.com/NMFR/optimize-css-assets-webpack-plugin). Setting `optimization.minimizer` overrides the defaults provided by webpack, so make sure to also specify a JS minimizer:
+
+**webpack.config.js**
+
+```js
+const UglifyJsPlugin = require("uglifyjs-webpack-plugin");
+const MiniCssExtractPlugin = require("mini-css-extract-plugin");
+const OptimizeCSSAssetsPlugin = require("optimize-css-assets-webpack-plugin");
+module.exports = {
+  optimization: {
+    minimizer: [
+      new UglifyJsPlugin({
+        cache: true,
+        parallel: true,
+        sourceMap: true // set to true if you want JS source maps
+      }),
+      new OptimizeCSSAssetsPlugin({})
+    ]
+  },
+  plugins: [
+    new MiniCssExtractPlugin({
+      filename: "[name].css",
+      chunkFilename: "[id].css"
+    })
+  ],
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [
+          MiniCssExtractPlugin.loader,
+          "css-loader"
+        ]
+      }
+    ]
+  }
+}
+```
+
 ### Features
 
 #### Using preloaded or inlined CSS