Merge pull request #172 from abraham/pwa

Add PWA

topics/pwa/index.md

@@ -0,0 +1,13 @@
+---
+aliases: progressive-web-app, progressive-web-apps
+created_by: Alex Russell and Frances Berriman
+display_name: PWA
+logo: pwa.png
+related: service-worker, offline, notifications, app-shell, manifest
+released: 2015
+short_description: Progressive Web Apps are traditional web sites that are enhanced with native like features.
+topic: pwa
+url: https://developers.google.com/web/progressive-web-apps/
+wikipedia_url: https://en.wikipedia.org/wiki/Progressive_web_app
+---
+Progressive Web Apps start with a traditional web site/application and progressively enhance with modern features. When sites are [secure](https://developers.google.com/web/fundamentals/security/encrypt-in-transit/why-https) they can leverage  [ServiceWorkers](https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API) to provider users with offline support, [Push notifications](https://developer.mozilla.org/en-US/docs/Web/API/Push_API) can help re-engage users, and [Web App Manifests](https://developer.mozilla.org/en-US/docs/Web/Manifest) let users install PWAs alongside native apps.