This PR improves the model card by:
1. Updating the `pipeline_tag` to `image-segmentation` to accurately reflect the model's application.
2. Linking to the paper ["Primus: Enforcing Attention Usage for 3D Medical Image Segmentation"](https://huggingface.co/papers/2503.01835).
3. Adding links to the official [nnU-Net](https://github.com/MIC-DKFZ/nnUNet) and [nnssl](https://github.com/MIC-DKFZ/nnssl) repositories.
4. Including the relevant BibTeX citations for the research.