Collapse the BibTeX in the data card citation

Shows a one-line citation and puts the BibTeX in a collapsed <details> block, so the long author list doesn't take up the end of the card.

README.md

@@ -91,7 +91,12 @@ Please report quality, risk, security vulnerabilities or NVIDIA AI Concerns [her
 
 ## Citation
 
-If you use OpenH-RF in your research, please cite the [OpenH-RF paper](https://arxiv.org/abs/2610.13616):
+If you use OpenH-RF in your research, please cite the paper:
+
+> T. S. W. Stevens et al., "OpenH-RF: A Large-Scale Ultrasound Raw Channel Dataset Initiative", arXiv:2610.13616, 2026. [arxiv.org/abs/2610.13616](https://arxiv.org/abs/2610.13616)
+
+<details>
+<summary>BibTeX</summary>
 
 ```bibtex
 @misc{stevens2026openhrf,
@@ -138,3 +143,5 @@ If you use OpenH-RF in your research, please cite the [OpenH-RF paper](https://a
   url = {https://arxiv.org/abs/2610.13616}
 }
 ```
+
+</details>