add serviceWorker

docs/index.html

@@ -17,4 +17,9 @@
   }
 </script>
 <script src="//unpkg.com/docsify/lib/docsify.min.js"></script>
+<script>
+  if (typeof navigator.serviceWorker !== 'undefined') {
+    navigator.serviceWorker.register('sw.js')
+  }
+</script>
 </html>