add preload.js script to electron main

public/index.html

@@ -11,6 +11,10 @@
     <noscript>
       <strong>We're sorry but <%= htmlWebpackPlugin.options.title %> doesn't work properly without JavaScript enabled. Please enable it to continue.</strong>
     </noscript>
+    <!-- <h1>Hello World!</h1>
+         We are using Node.js <span id="node-version"></span>, Chromium
+         <span id="chrome-version"></span>, and Electron
+         <span id="electron-version"></span>. -->
     <div id="app"></div>
     <!-- built files will be auto injected -->
   </body>