Travis CI: added badge to README.

Author: cknitt

README.md

@@ -1,5 +1,7 @@
 # bs-react-intl-extractor
 
+[![Build Status](https://travis-ci.org/cknitt/bs-react-intl-extractor.svg?branch=master)](https://travis-ci.org/cknitt/bs-react-intl-extractor)
+
 Extracts messages for localization from [Reason] source files.
 
 This assumes that you are using the [bs-react-intl] bindings for [react-intl]