github: add issue template stable release notice

.github/ISSUE_TEMPLATE.md

@@ -1,7 +1,11 @@
 <!--
 
-Are you using a third party tool (e.g. clairctl, klar)?
-If so, please open issues with them first.
+The Clair developers only support the Clair API.
+They do not support or operate any third party client (e.g. clairctl, klar, harbor).
+If you are using a third party client, please create issues on their respective repositories.
+
+Are you using a development build of Clair (e.g. quay.io/coreos/clair-git)?
+Your problem might be solved by switching to a stable release (e.g. quay.io/coreos/clair).
 
 -->
 
@@ -15,9 +19,10 @@ If so, please open issues with them first.
 
 
 **Environment**:
-- Clair version/image:
-- Host OS:
-- Kernel (e.g. `uname -a`):
-- Kubernetes version (use `kubectl version`):
-- Helm version (use `helm version`):
-- Network/Firewall setup:
+- Clair version/image: 
+- Clair client name/version: 
+- Host OS: 
+- Kernel (e.g. `uname -a`): 
+- Kubernetes version (use `kubectl version`): 
+- Helm version (use `helm version`): 
+- Network/Firewall setup: