Add code coverage badge.

README.rst

@@ -1,7 +1,7 @@
 LAKEsuperior
 ============
 
-|build status| |docs| |pypi|
+|build status| |docs| |pypi| |codecov|
 
 LAKEsuperior is an alternative `Fedora
 Repository <http://fedorarepository.org>`__ implementation.
@@ -65,7 +65,12 @@ including installation instructions.
 .. |docs| image:: https://readthedocs.org/projects/lakesuperior/badge/
     :alt: Documentation Status
     :target: https://lakesuperior.readthedocs.io/en/latest/?badge=latest
-    
+
 .. |pypi| image:: https://badge.fury.io/py/lakesuperior.svg
     :alt: PyPI Package
     :target: https://badge.fury.io/py/lakesuperior
+
+.. |codecov| image:: https://codecov.io/gh/scossu/lakesuperior/branch/master/graph/badge.svg
+  :alt: Code coverage
+  :target: https://codecov.io/gh/scossu/lakesuperior
+