docs: optimizations documentation

docs/README.md

@@ -66,6 +66,7 @@ kb_sync_latest_only
   - [Guide - Hybrid Approach and ICM URL Rewriting](./guides/hybrid-approach-icm-url-rewriting.md)
 - [Concept - Logging](./concepts/logging.md)
 - [Guide - CI](./guides/continuous-integration.md)
+- [Guide - Optimizations](./guides/optimizations.md)
 
 ### Third-party Integrations
 

docs/guides/optimizations.md

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+<!--
+kb_guide
+kb_pwa
+kb_everyone
+kb_sync_latest_only
+-->
+
+# Optimizations
+
+## Nginx Optimizations
+
+The Nginx building block applies:
+
+- Compression of responses
+- PageSpeed optimization
+
+for further information, please refer to the [Guide - Building and Running nginx][nginx-startup].
+
+## Custom Webpack Build
+
+The PWA uses a customized webpack build, that opens the doors to additional optimizations.
+The build can be customized in the file [`webpack.custom.ts`](../../templates/webpack/webpack.custom.ts).
+
+If the PWA is built using `production` configuration. (Either by building with `--configuration=<other>,production` or by building the docker image with `--build-arg configuration=<other>,production`), the following optimizations are applied:
+
+- Angular CLI [build-optimizer](https://github.com/angular/angular-cli/tree/master/packages/angular_devkit/build_optimizer#angular-build-optimizer)
+- Webpack [SplitChunksPlugin](https://webpack.js.org/plugins/split-chunks-plugin/) is instructed to produce only `main`, `vendor`, `polyfills` and one `common` bundle for the code for optimized compression and download of the application.
+- All `data-testing` attributes are removed from the HTML templates to reduce output.
+
+## CSS Optimization
+
+On npm `postbuild`, we integrated [PurgeCSS](https://purgecss.com) to remove unused CSS classes from the CSS output.
+[Configuration](https://purgecss.com/configuration.html), especially whitelisting certain classes, can be done in [`purgecss.config.js`](../../purgecss.config.js).
+
+# Further References
+
+- [Guide - Building and Running nginx Docker Image][nginx-startup]
+
+[nginx-startup]: ./nginx-startup.md