docs: add documentation for progressive web app features

docs/README.md

@@ -39,6 +39,7 @@ kb_sync_latest_only
 
 ### Customization
 
+- [Concept - Progressive Web App](./concepts/progressive-web-app.md)
 - [Guide - Customizations](./guides/customizations.md)
   - [Guide - Multiple Themes](./guides/multiple-themes.md)
 - [Guide - Migration](./guides/migrations.md)

docs/concepts/progressive-web-app.md

@@ -0,0 +1,34 @@
+<!--
+kb_concepts
+kb_pwa
+kb_everyone
+kb_sync_latest_only
+-->
+
+# Progressive Web App
+
+In order to be a [Progressive Web Application](https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps), the Intershop PWA implements some advanced concepts matching those criteria.
+
+## Web App Manifest
+
+The Web App Manifest enables the PWA to be installable on home screens of mobile devices.
+The application is easily accessible via a generated link and branding is applied to icons and browser colouring so it poses as a native application.
+
+The manifest in the PWA is theme specific and can be customized in the file `src/assets/themes/<theme>/manifest.webmanifest`.
+
+## Service Worker
+
+Service workers are automatically installed into client device browsers and take over the handling of the application on the client side.
+Possible advanced features supplied are offline-capabilities and push notifications.
+After installation, the service worker effectively disables server-side rendering for clients and invokes all rendering on the client himself.
+
+For the Intershop PWA, offline browsing is not a suitable use-case for most customers and push notifications are not yet supplied by the Commerce Management Suite.
+For now service worker integration is an **experimental** feature that can be activated for appropriate projects.
+
+To activate the service worker run
+
+```bash
+node schematics/customization/service-worker true
+```
+
+You can also activate the service worker specifically for docker builds by supplying the build argument `serviceWorker=true`.