Update example playbook in README
Update example playbook in README

The vars_prompt section is needed to get the grub password.

shepdelacreme/RHEL6-STIG,lmasiero/RHEL6-STIG,dkadow/RHEL6-STIG,samdoran/ansible-role-rhel6stig,codexchee/RHEL6-STIG,bbaassssiiee/RHEL6-STIG,samdoran/ansible-role-rhel6stig,bbaassssiiee/RHEL6-STIG,shepdelacreme/RHEL6-STIG,defionscode/RHEL6-STIG,MindPointGroup/RHEL6-STIG,MindPointGroup/RHEL6-STIG,defionscode/RHEL6-STIG,dkadow/SLES11-STIG