readme: add build status for master branch

Author: Kátia Nakamura

README.md

@@ -1,2 +1,3 @@
-# pyconbalkan
+# pyconbalkan [![Build Status](https://travis-ci.org/PythonBalkan/pyconbalkan.svg?branch=master)](https://travis-ci.org/PythonBalkan/pyconbalkan)
+
 Website for PyCon Balkan