Updated README.md

README.md

 ## WebSSH
 [![Build Status](https://travis-ci.org/huashengdun/webssh.svg?branch=master)](https://travis-ci.org/huashengdun/webssh)
+[![codecov](https://codecov.io/gh/huashengdun/webssh/branch/master/graph/badge.svg)](https://codecov.io/gh/huashengdun/webssh)
 ![license](https://img.shields.io/github/license/mashape/apistatus.svg)
 
 A simple web application to be used as an ssh client to connect to your ssh servers. It is written in Python, base on tornado and paramiko.