Add section for security vulnerabilities to new issue template.

Fixes elastic#9283

.github/ISSUE_TEMPLATE.md

@@ -1,5 +1,8 @@
 Please post all product and debugging questions on our [forum](https://discuss.elastic.co/c/logstash). Your questions will reach our wider community members there, and if we confirm that there is a bug, then we can open a new issue here.
 
+For security vulnerabilities please only send reports to [email protected].
+See https://www.elastic.co/community/security for more information.
+
 Logstash Plugins are located in a different organization: https://github.com/logstash-plugins. For bugs on specific Logstash plugins, for example, if Redis Output has a defect, please open it in the respective Redis Output repository. 
 
 For all general issues, please provide the following details for fast resolution: