Add Codecov badge to README

Added Codecov badge to README for coverage tracking.

Author: GlobalHive

README.md

@@ -8,6 +8,7 @@
 [![version](https://img.shields.io/npm/v/@globalhive/vuejs-tour)](https://www.npmjs.com/package/@globalhive/vuejs-tour)
 [![downloads](https://img.shields.io/npm/dt/@globalhive/vuejs-tour)](https://www.npmjs.com/package/@globalhive/vuejs-tour)
 [![producthunt](https://img.shields.io/badge/view_on-ProductHunt-orange)](https://www.producthunt.com/products/vuejs-tour)
+[![codecov](https://codecov.io/gh/GlobalHive/vuejs-tour/graph/badge.svg?token=CUET0CGLU9)](https://codecov.io/gh/GlobalHive/vuejs-tour)
 
 > VueJS Tour is a lightweight, simple and customizable tour plugin.
 > It provides a quick and easy way to guide your users through your application.