fix(template/typescript-webpack): magic constant is a string w/commen…

…ts about what it's for (#2166)

packages/template/typescript-webpack/tmpl/index.ts

@@ -1,5 +1,8 @@
 import { app, BrowserWindow } from 'electron';
-declare const MAIN_WINDOW_WEBPACK_ENTRY: any;
+// This allows TypeScript to pick up the magic constant that's auto-generated by Forge's Webpack
+// plugin that tells the Electron app where to look for the Webpack-bundled app code (depending on
+// whether you're running in development or production).
+declare const MAIN_WINDOW_WEBPACK_ENTRY: string;
 
 // Handle creating/removing shortcuts on Windows when installing/uninstalling.
 if (require('electron-squirrel-startup')) { // eslint-disable-line global-require