fix(README): add citation

README.md

@@ -65,4 +65,15 @@ Please note that the images are subject to the [Terms of Use of MS COCO-2017](ht
 
 > **Images**
 >
-> The COCO Consortium does not own the copyright of the images. Use of the images must abide by the Flickr Terms of Use. The users of the images accept full responsibility for the use of the dataset, including but not limited to the use of any copies of copyrighted images that they may create from the dataset.
+> The COCO Consortium does not own the copyright of the images. Use of the images must abide by the Flickr Terms of Use. The users of the images accept full responsibility for the use of the dataset, including but not limited to the use of any copies of copyrighted images that they may create from the dataset.
+
+## BibTeX
+
+```
+@article{zhang2025sphere,
+  title={SPHERE: Unveiling Spatial Blind Spots in Vision-Language Models Through Hierarchical Evaluation},
+  author={Zhang, Wenyu and Ng, Wei En and Ma, Lixin and Wang, Yuwen and Zhao, Jungqi and Koenecke, Allison and Li, Boyang and Wang, Lu},
+  journal={arXiv},
+  year={2025}
+}
+```