Add pullreview badge.

README.md

@@ -25,6 +25,8 @@
 
 * [![Coverage Status](https://coveralls.io/repos/gitlabhq/gitlabhq/badge.png?branch=master)](https://coveralls.io/r/gitlabhq/gitlabhq)
 
+* [![PullReview stats](https://www.pullreview.com/gitlab/gitlab-org/gitlab-ce/badges/master.svg?)](https://www.pullreview.com/gitlab.gitlab.com/gitlab-org/gitlab-ce/reviews/master)
+
 ### Resources
 
 * [GitLab.com](https://www.gitlab.com/) includes information about [subscriptions](https://www.gitlab.com/subscription/), [consultancy](https://www.gitlab.com/consultancy/), the [community](https://www.gitlab.com/community/) and the [hosted GitLab Cloud](https://www.gitlab.com/cloud/).