Add coveragerc and badge.

.coveragerc

@@ -0,0 +1,7 @@
+[report]
+exclude_lines =
+    pragma: no cover
+    def __repr__
+    raise AssertionError
+    raise NotImplementedError
+    if __name__ == .__main__.:

README.rst

@@ -5,6 +5,10 @@ Sigal - Simple Static Gallery Generator
    :target: https://travis-ci.org/saimn/sigal
    :alt: Travis-ci: continuous integration status.
 
+.. image:: https://coveralls.io/repos/saimn/sigal/badge.png?branch=master
+   :target: https://coveralls.io/r/saimn/sigal?branch=master
+   :alt: coveralls.io
+
 Sigal is yet another simple static gallery generator. It's written in Python
 and it allows to build a static gallery of images with the following features: