Add pipeline tag, paper, and code links

This PR improves the model card by:

- Adding the `pipeline_tag: image-classification`, which will make the model discoverable at https://huggingface.co/models?pipeline_tag=image-classification.
- Adding a link to the paper: [DART: Differentiable Dynamic Adaptive Region Tokenizer for Vision Transformer and Mamba](https://huggingface.co/papers/2506.10390).
- Adding a link to the official GitHub repository: https://github.com/HCPLab-SYSU/DART.

Please review these changes.

README.md

@@ -1,3 +1,8 @@
----
-license: apache-2.0
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+---
+license: apache-2.0
+pipeline_tag: image-classification
+---
+
+This repository contains models described in the paper [DART: Differentiable Dynamic Adaptive Region Tokenizer for Vision Transformer and Mamba](https://huggingface.co/papers/2506.10390).
+
+Code: https://github.com/HCPLab-SYSU/DART