add web-serial-polyfill to support flashing from android devices

index.html

@@ -224,6 +224,14 @@
 
 </div>
 
+<!-- setup web-serial-polyfill -->
+<script type="module">
+    import { serial } from "./js/web-serial-polyfill@1.0.15/dist/serial.js";
+    if(!navigator.serial && navigator.usb){
+        navigator.serial = serial;
+    }
+</script>
+
 <!-- setup esptool-js -->
 <script type="module">
     import { ESPLoader, Transport } from "./js/esptool-js@0.4.5/bundle.js";