docs: fix for Webpack output.library and libraryTarget: 'window' (#212)

When building a library and use a multi entry config, only the last item in the entry array will be exposed. The example that was provided by the plugin would expose the webpack plugin serve client in the end file and it breaks the app

Author: zauan

README.md

@@ -65,8 +65,8 @@ const options = { ... };
 module.exports = {
 	// an example entry definition
 	entry: [
-		'app.js',
 		'webpack-plugin-serve/client' // ← important: this is required, where the magic happens in the browser
+		'app.js'
 	]
   ...
   plugins: [