Sync the set of badges in the README with the docs index page.

README.md

@@ -6,6 +6,7 @@ Extensible BDD assertion toolkit
 [![Build Status](https://github.com/unexpectedjs/unexpected/workflows/Tests/badge.svg)](https://travis-ci.org/unexpectedjs/unexpected)
 [![Coverage Status](https://coveralls.io/repos/unexpectedjs/unexpected/badge.svg)](https://coveralls.io/r/unexpectedjs/unexpected)
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/unexpectedjs/unexpected?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+[![Github](https://img.shields.io/github/stars/unexpectedjs/unexpected.svg?label=Star&maxAge=2592000&style=flat)](https://github.com/unexpectedjs/unexpected)
 [![BrowserStack Status](https://www.browserstack.com/automate/badge.svg?badge_key=cjVWSDFIaERKWVdxc2s5bStaY08vMUFwbW1NbTdzZHJmVXBCUjBlemo3Yz0tLU5iL3I0L3Z4elVhZjBTbWtvbmpHRnc9PQ==--692805fea09bec4c4ea7c898fa9208a0fa61283e)](https://www.browserstack.com/automate/public-build/cjVWSDFIaERKWVdxc2s5bStaY08vMUFwbW1NbTdzZHJmVXBCUjBlemo3Yz0tLU5iL3I0L3Z4elVhZjBTbWtvbmpHRnc9PQ==--692805fea09bec4c4ea7c898fa9208a0fa61283e)
 
 Read [the documentation](https://unexpected.js.org/).