docs: Update the security e-mail address.

This repository is now managed by the Axim Collaborative and security issues
with it should be reported to security@openedx.org instead of security@edx.org

This work is being done as a part of openedx/wg-security#16

Author: feanil

README.rst

@@ -85,7 +85,7 @@ People
 Reporting Security Issues
 *************************
 
-Please do not report security issues in public. Please email security@edx.org.
+Please do not report security issues in public. Please email security@openedx.org.
 
 .. |ci-provisioning-badge| image:: https://github.com/openedx/devstack/actions/workflows/provisioning-tests.yml/badge.svg?branch=master
     :target: https://github.com/openedx/devstack/actions/workflows/provisioning-tests.yml