README.rst: Add a badge for the Travis CI status. [ci skip]

Author: jakirkham

README.rst

@@ -1,3 +1,7 @@
+|Travis CI Status|
+
+-----------------------------------------------------------------------------------------------------
+
 Python-bioformats is a Python wrapper for Bio-Formats, a standalone
 Java library for reading and writing life sciences image file
 formats. Bio-Formats is capable of parsing both pixels and metadata
@@ -20,3 +24,7 @@ python-bioformats is licensed under the GNU General Public License
 See the accompanying files COPYING and LICENSE for details.
 
 Copyright (c) 2009-2014 Broad Institute. All rights reserved.
+
+
+.. |Travis CI Status| image:: https://travis-ci.org/CellProfiler/python-bioformats.svg?branch=master
+   :target: https://travis-ci.org/CellProfiler/python-bioformats