rbler/OST-Bench · Improve dataset card: Update license, size category, task category, and code link

This PR improves the dataset card for OST-Bench by:

Updating the license to the specific cc-by-nc-4.0 based on the GitHub repository's license information.
Refining the size_categories to 10K<n<100K to accurately reflect the dataset's 10,000 examples.
Adding image-text-to-text to task_categories for better discoverability, complementing the existing specific VQA tasks.
Fixing a typo in the introductory sentence ("Unstanding" to "Understanding").
Unifying the "Code" link to https://github.com/rbler1234/OST-Bench for consistency with the project's GitHub README and evaluation instructions.