docs(README.md): add notice of final release and maintenance mode

Author: mboersma

README.md

@@ -1,3 +1,9 @@
+
+|![](https://upload.wikimedia.org/wikipedia/commons/thumb/1/17/Warning.svg/156px-Warning.svg.png) | Deis Workflow will soon no longer be maintained.<br />Please [read the announcement](https://deis.com/blog/2017/deis-workflow-final-release/) for more detail. |
+|---:|---|
+| 09/07/2017 | Deis Workflow [v2.18][] final release before entering maintenance mode |
+| 03/01/2018 | End of Workflow maintenance: critical patches no longer merged |
+
 # Deis Registry Proxy
 
 Deis (pronounced DAY-iss) Workflow is an open source Platform as a Service (PaaS) that adds a developer-friendly layer to any [Kubernetes](http://kubernetes.io) cluster, making it easy to deploy and manage applications on your own servers.
@@ -28,3 +34,4 @@ When you've built your new feature or fixed a bug, make sure you've added approp
 [issues]: https://github.com/deis/registry-proxy/issues
 [prs]: https://github.com/deis/registry-proxy/pulls
 [registry]: https://github.com/deis/registry
+[v2.18]: https://github.com/deis/workflow/releases/tag/v2.18.0