Add website deadlink check badge

Author: nicolasstucki

README.md

@@ -3,6 +3,7 @@ Dotty
 [![Build Status](http://dotty-ci.epfl.ch/api/badges/lampepfl/dotty/status.svg)](http://dotty-ci.epfl.ch/lampepfl/dotty)
 [![Join the chat at https://gitter.im/lampepfl/dotty](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/lampepfl/dotty?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Log Knowledge](https://img.shields.io/badge/log-knowledge-blueviolet.svg)](https://github.com/lampepfl/dotty-knowledge/issues/new/choose)
+[![Build Status](https://travis-ci.org/nicolasstucki/dotty-website-linkcheck.svg?branch=master)](https://travis-ci.org/nicolasstucki/dotty-website-linkcheck)
 
 * [Homepage](http://dotty.epfl.ch)
 * [Documentation](http://dotty.epfl.ch/docs)