Point to github discussion in issue template (#4491)

A generic question might be more suited for a discussion, add pointer to
the issue template.
Signed-off-by: Miek Gieben <miek@miek.nl>

.github/ISSUE_TEMPLATE/question.md

@@ -4,4 +4,7 @@ about: A question related to CoreDNS
 labels: question
 
 ---
-<!-- Please only use this template for submitting a generic question -->
+<!--
+Please only use this template for submitting a generic question.
+Or consider using a GitHub discussion https://github.com/coredns/coredns/discussions
+-->