Register a service worker

To make installing as a PWA possible. Fixes #1181.

src/browser/register.ts

@@ -0,0 +1,14 @@
+import { getOptions, normalize } from "../common/util"
+
+const options = getOptions()
+
+if ("serviceWorker" in navigator) {
+  const path = normalize(`${options.base}/static-${options.commit}/dist/serviceWorker.js`)
+  navigator.serviceWorker
+    .register(path, {
+      scope: options.base || "/",
+    })
+    .then(function() {
+      console.log("[Service Worker] registered")
+    })
+}