Update security.rst with e-mail and local link to security.rst

Author: beberlei

SECURITY.md

@@ -12,6 +12,10 @@ understand the assumptions we make.
 
 - [DBAL Security Page](https://www.doctrine-project.org/projects/doctrine-dbal/en/stable/reference/security.html)
 - [ORM Security Page](https://www.doctrine-project.org/projects/doctrine-orm/en/stable/reference/security.html)
+- [security.rst page in this repository](docs/en/reference/security.rst)
 
 If you find a Security bug in Doctrine, please follow our
 [Security reporting guidelines](https://www.doctrine-project.org/policies/security.html#reporting).
+
+Security vulnerabilities should be reported to security@doctrine-project.org
+and not posted on the GitHub issue tracker of the project.