Update the readme for ServiceWorker terminology.
Update the readme for ServiceWorker terminology.

justinleoye/ServiceWorker,justinleoye/ServiceWorker,mkruisselbrink/ServiceWorker,martinthomson/ServiceWorker,karolklp/ServiceWorker,zuzusik/ServiceWorker,justinleoye/ServiceWorker,karolklp/ServiceWorker,slightlyoff/ServiceWorker,slightlyoff/ServiceWorker,chadoliver/ServiceWorker,zuzusik/ServiceWorker,karolklp/ServiceWorker,chadoliver/ServiceWorker,martinthomson/ServiceWorker,chadoliver/ServiceWorker,mkruisselbrink/ServiceWorker,zuzusik/ServiceWorker,martinthomson/ServiceWorker