Add link to security page

Because some people do not think…

issue_template.md

@@ -3,6 +3,8 @@ Thanks for reporting issues back to ownCloud! This is the issue tracker of ownCl
 
 This is the bug tracker for the Server component. Find other components at https://github.com/owncloud/core/blob/master/CONTRIBUTING.md#guidelines
 
+For reporting potential security issues please see https://owncloud.org/security/
+
 To make it possible for us to help you please fill out below information carefully.
 --> 
 ### Steps to reproduce