Issue #3094817 by nicxvan, quietone, prudloff: Add a SECURITY.md explaining...

Issue #3094817 by nicxvan, quietone, prudloff: Add a SECURITY.md explaining how to report security vulnerabilities properly

(cherry picked from commit 6603a36d)

SECURITY.md

+# Drupal Security Policy
+
+If you discover a security vulnerability in Drupal core or a contributed project
+(module, theme, or distribution) keep it confidential and [report it to the Drupal security team](https://www.drupal.org/docs/develop/issues/issue-procedures-and-etiquette/reporting-a-security-issue).