Scripts: Add CHANGELOG notes for optimized Webpack configuration

See: #14860

Author: aduth

packages/scripts/CHANGELOG.md

@@ -5,6 +5,12 @@
 - Leverage `@wordpress/dependency-extraction-webpack-plugin` plugin to extract WordPress
   dependencies.
 
+### Enhancements
+
+- The default Webpack configuration uses [`thread-loader`](https://github.com/webpack-contrib/thread-loader) to parallelize Babel processing.
+- The default Webpack configuration now opts-in to [the `cacheDirectory` option](https://webpack.js.org/loaders/babel-loader/#options) for its Babel loader.
+- The `source-map-loader` is excluded from production builds. This serves only as an optimization and should otherwise have no impact on build results.
+
 ## 3.1.0 (2019-03-20)
 
 ## New features