Update simple-acl-controlled-application.rst

What I did
http://book.cakephp.org/view/1547/Acts-As-a-Requester
Followed the books docs on creating user and group models
setup my user model to use the bindNode function defined, so that user aros are not created

What happened
i add groups and they insert their correct aros
but when i add users, aros are still created

What I expected to happen
Only group aros to be created, not user ones.