Update README: add travis build status

Author: ggreg

README.rst

@@ -1,3 +1,5 @@
+.. image:: https://travis-ci.org/botify-labs/python-simple-workflow.png?branch=develop   :target: https://travis-ci.org/botify-labs/python-simple-workflow
+
 ======================
 Python Simple Workflow
 ======================
@@ -27,4 +29,4 @@ Installation
 Usage and all the rest
 ======================
 
-Please, refer to `Documentation <http://python-simple-workflow.readthedocs.org>`_
+Please, refer to `Documentation <http://python-simple-workflow.readthedocs.org>`_