added docs for CreateBundle rest_force_request_locale config option

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes (https://github.com/symfony-cmf/CreateBundle/pull/122)
| Applies to    | all (or 1.2+)
| Fixed tickets | -
@WouterJ do you have a tipp for me here?