Added a note about the security advisories database

Author: javiereguiluz

contributing/code/security.rst

@@ -38,6 +38,8 @@ confirmed, the core-team works on a solution following these steps:
 #. Publish the post on the official Symfony `blog`_ (it must also be added to
    the "`Security Advisories`_" category);
 #. Update the security advisory list (see below).
+#. Update the public `security advisories database`_ maintained by the
+   FriendsOfPHP organization and which is used by the ``security:check`` command.
 
 .. note::