doc(deploying-apps.md): add note about known issue in controller (#395)

when deployments are turned on, the controller can crash on startup in
a very specific case

Ref deis/controller#903

* doc(deploying-apps.md): add note about known issue

Author: arschles

src/applications/deploying-apps.md

@@ -100,6 +100,15 @@ Where you will see differences while using the CLI is `deis ps:list` will output
 Behind the scenes your application deploy will be built up of a Deployment object per process type,
 each having multiple ReplicaSets (one per release) which in turn manage the Pods running your application.
 
+!!! Known Issue
+		If `DEIS_KUBERNETES_DEPLOYMENTS` is enabled and there is a deployment in progress when the
+		controller starts, the controller will crash until the deployment is finished. This issue can
+		specifically manifest itself if the controller crashes while you are scaling an app.
+		Kubernetes will automatically restart the controller, but it will not start back up properly
+		until the scale operation (which will complete in the background) completes.
+		We intend to fix this issue soon and are tracking the work in
+		[https://github.com/deis/controller/issues/903](https://github.com/deis/controller/issues/903).
+
 [install client]: ../users/cli.md#installation
 [application]: ../reference-guide/terms.md#application
 [controller]: ../understanding-workflow/components.md#controller