Fixed OptionsResolver component docs

I finally applied the comments of https://github.com/symfony/symfony-docs/pull/2547#issuecomment-16993740

| Q   | A
| --- | ---
| Doc fix? | yes
| New docs? | no
| Applies to | 2.1+
| Fixed tickets | https://github.com/symfony/symfony-docs/pull/2547#issuecomment-16993740