add MenuOptionsInterface docs

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | dev
| Fixed tickets | https://github.com/symfony-cmf/MenuBundle/pull/197
there already is a menus.rst file in the git repo https://github.com/symfony-cmf/symfony-cmf-docs/blob/dev/bundles/simple_cms/menus.rst

this is probably why we have a conflict with this PR.

can you please try to solve this so git only sees you adding the tip and not the whole file? (actually not sure how this can happen, if you also don't know we have to find some solution).