[README.md] Add build status bagde

README.md

@@ -1,3 +1,5 @@
+[![Build Status](https://travis-ci.org/rg3/youtube-dl.svg?branch=master)](https://travis-ci.org/rg3/youtube-dl)
+
 youtube-dl - download videos from youtube.com or other video platforms
 
 - [INSTALLATION](#installation)