Add preview

Author: adamlaki

.github/root-preview-mockup.png

@@ -12,6 +12,8 @@
 
 **This repository contains the static template of our Laravel admin named [Root](https://root.conedevelopment.com/).**
 
+![The preview image of the template.](./.github/root-preview-mockup.png)
+
 The template is built with Eleventy for our sanity and easier management. You can grab the content from the Nunjucks template files or the compiled `dist` folder.
 
 The template will probably change regularly in the future because of the Laravel package development.