Merge pull request #4000 from xiang90/production_users

README: link to production users

README.md

@@ -17,7 +17,7 @@ etcd is a distributed, consistent key-value store for shared configuration and s
 
 etcd is written in Go and uses the [Raft][raft] consensus algorithm to manage a highly-available replicated log.
 
-etcd is used in production by many companies, and the development team stands behind it in critical deployment scenarios, where etcd is frequently teamed with applications such as [Kubernetes][k8s], [fleet][fleet], [locksmith][locksmith], [vulcand][vulcand], and many others.
+etcd is used [in production by many companies](./Documentation/production-users.md), and the development team stands behind it in critical deployment scenarios, where etcd is frequently teamed with applications such as [Kubernetes][k8s], [fleet][fleet], [locksmith][locksmith], [vulcand][vulcand], and many others.
 
 See [etcdctl][etcdctl] for a simple command line client.
 Or feel free to just use `curl`, as in the examples below.