change offerings for issue templates

ref #251 (comment)

Author: 2bndy5

.github/ISSUE_TEMPLATE/config.yml

@@ -6,3 +6,6 @@ contact_links:
   - name: cpp-linter discussions
     url: https://github.com/orgs/cpp-linter/discussions
     about: A place for feedback not specific to cpp-linter-action
+  - name: Maintainers' note
+    url: https://github.com/cpp-linter/cpp-linter-action/issues/new
+    about: Start a discussion for maintainers only