updated docs

Resources/doc/reference/security.rst

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+Security
+========
+
+See the security part in the documentation of the Admin bundle. When using ACL, the object ACL's need to be created
+to have the ACL implementation working correctly. Otherwise access can be denied because the access rules are not found
+for an object.
+
+If you have Admin classes, you can generate the object ACL rules for each object of an admin:
+
+.. code-block:: sh
+
+    $ php app/console sonata:admin:generate-object-acl
+
+Optionally, you can specify an object owner, this will be asked when the command is run.