docs: update readme badgets

Author: icebob

README.md

@@ -3,6 +3,8 @@ A schema-based form generator component for Vue.js
 
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/912039aa815e40de8315032519aa7e6c)](https://www.codacy.com/app/mereg-norbert/vue-form-generator?utm_source=github.com&utm_medium=referral&utm_content=icebob/vue-form-generator&utm_campaign=Badge_Grade)
 [![Build Status](https://travis-ci.org/icebob/vue-form-generator.svg?branch=master)](https://travis-ci.org/icebob/vue-form-generator)
+[![Coverage Status](https://coveralls.io/repos/github/icebob/vue-form-generator/badge.svg?branch=master)](https://coveralls.io/github/icebob/vue-form-generator?branch=master)
+
 [![Dependency Status](https://david-dm.org/icebob/vue-form-generator.svg)](https://david-dm.org/icebob/vue-form-generator)
 [![devDependency Status](https://david-dm.org/icebob/vue-form-generator/dev-status.svg)](https://david-dm.org/icebob/vue-form-generator#info=devDependencies)
 [![Downloads](https://img.shields.io/npm/dt/vue-form-generator.svg)](https://www.npmjs.com/package/vue-form-generator)