github: add issue template

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,23 @@
+<!--
+
+Are you using a third party tool (e.g. clairctl, klar)?
+If so, please open issues with them first.
+
+-->
+
+**Description of Problem**:
+
+
+**Expected Outcome**:
+
+
+**Actual Outcome**:
+
+
+**Environment**:
+- Clair version/image:
+- Host OS:
+- Kernel (e.g. `uname -a`):
+- Kubernetes version (use `kubectl version`):
+- Helm version (use `helm version`):
+- Network/Firewall setup: