add file input to load cart from filesystem

web/src/index.html

@@ -7,6 +7,7 @@
     <body>
         <canvas id="screen" width="320" height="256"></canvas>
         <div id="message"></div>
+        <input id="cart" type="file" accept=".wasm,.uw8,application/wasm">
         <script type="module">
             import "./main.js";
         </script>