Add codecov badge to the Readme.md

Author: Jakub

README.md

@@ -15,6 +15,7 @@
 <hr />
 
 [![Actions Status](https://github.com/sandstreamdev/react-swipeable-list/workflows/Node%20CI/badge.svg)](https://github.com/sandstreamdev/react-swipeable-list/actions)
+[![codecov](https://codecov.io/gh/sandstreamdev/react-swipeable-list/branch/master/graph/badge.svg)](https://codecov.io/gh/sandstreamdev/react-swipeable-list)
 ![GitHub Release Date](https://img.shields.io/github/release-date/sandstreamdev/react-swipeable-list)
 [![All Contributors](https://img.shields.io/badge/all_contributors-6-orange.svg?style=flat-square)](#contributors)
 ![License: MIT](https://img.shields.io/github/license/sandstreamdev/react-swipeable-list)