deprecation notice for pure docker

Author: DaedalusG

README.md

@@ -31,6 +31,8 @@ We've made our deployment configurations open source to better serve our custome
 
 ## Pure-Docker Sourcegraph cluster deployment reference
 
+> ⚠️ **Deprecation Notice:** The pure-Docker deployment method is planned for deprecation.
+
 What if your organization wants a multi-machine deployment without using Kubernetes?
 What if you use a different container management platform, for example?
 Anyone using a container management platform other than Kubernetes (Netflix's [Titus](https://netflix.github.io/titus/), Apache's [Mesos](http://mesos.apache.org/documentation/latest/docker-containerizer/), etc.) can use our [Pure-Docker Sourcegraph cluster deployment reference](./pure-docker/README.md) to deploy Sourcegraph.

pure-docker/README.md

@@ -1,5 +1,7 @@
 # Pure-Docker Sourcegraph cluster deployment reference
 
+> ⚠️ **Deprecation Notice:** The pure-Docker deployment method is planned for deprecation.
+
 ## Deploying
 
 First clone the repository, then: