Added service worker and site caching

src/index.tsx

@@ -1,5 +1,6 @@
 import React from "react";
 import ReactDOM from "react-dom";
+import * as ServiceWorker from "./registerServiceWorker";
 
 import "./index.css";
 
@@ -12,3 +13,4 @@ ReactDOM.render(
   document.getElementById("root")
 );
 
+ServiceWorker.register();