ng add @angular/pwa
References
https://medium.com/poka-techblog/turn-your-angular-app-into-a-pwa-in-4-easy-steps-543510a9b626
https://blog.angulartraining.com/how-to-go-offline-with-angular-service-worker-a3cc5dabc4d5
https://developers.google.com/web/fundamentals/app-install-banners/