Add dataset card, link to paper, task category

This PR ensures the dataset can be found at https://huggingface.co/papers/2503.19653 and is tagged as an image classification dataset.
It also adds a link to the Github repository.

README.md

@@ -24,4 +24,11 @@ configs:
   data_files:
   - split: sd15
     path: data/sd15-*
+task_categories:
+- image-classification
+license: cc-by-sa-4.0
 ---
+
+This repository contains the OpenSDI training dataset, presented in the paper [OpenSDI: Spotting Diffusion-Generated Images in the Open World](https://huggingface.co/papers/2503.19653).
+
+Code: https://github.com/iamwangyabin/OpenSDI