This PR improves the dataset card for `OpenMMReasoner` by:
- Adding `task_categories` (`image-text-to-text`) and relevant `tags` (`sft`, `reinforcement-learning`) to the YAML metadata, improving discoverability.
- Adding the `license` (CC-BY-NC-4.0) to the YAML metadata.
- Incorporating a detailed "Overview" section using the paper's abstract to provide a richer description of the dataset's context and methodology.
All existing links and sample usage instructions have been preserved.
