Add coverage support.
diff --git a/README.rst b/README.rst
index b9e300f..97acd60 100644
--- a/README.rst
+++ b/README.rst
@@ -6,6 +6,11 @@
     :target: https://travis-ci.org/google/yapf
     :alt: Build status
 
+
+.. image:: https://coveralls.io/repos/google/yapf/badge.svg?branch=master
+    :target: https://coveralls.io/r/google/yapf?branch=master
+    :alt: Coverage status
+
 Introduction
 ============