Add bibtex citation info

Adding this will also link this dataset to the paper on the Hub: https://huggingface.co/papers/2401.11814

README.md

@@ -88,7 +88,16 @@ mit
 
 When using the data please cite : 
 
-**authors papers coming soon** 
+```bibtext
+@misc{gucciardi2024symbrain,
+      title={Symbrain: A large-scale dataset of MRI images for neonatal brain symmetry analysis}, 
+      author={Arnaud Gucciardi and Safouane El Ghazouali and Francesca Venturini and Vida Groznik and Umberto Michelucci},
+      year={2024},
+      eprint={2401.11814},
+      archivePrefix={arXiv},
+      primaryClass={cs.CV}
+}
+```
 
 and