docs(bib): add deltaflow bib back.

Author: Kin-Zhang

README.md

@@ -349,6 +349,12 @@ If you find it useful, please cite our works:
     year={2025},
     journal={arXiv preprint arXiv:2503.00803},
 }
+@article{zhang2025deltaflow,
+    title={{DeltaFlow}: An Efficient Multi-frame Scene Flow Estimation Method},
+    author={Zhang, Qingwen and Zhu, Xiaomeng and Zhang, Yushan and Cai, Yixi and Andersson, Olov and Jensfelt, Patric},
+    year={2025},
+    journal={arXiv preprint arXiv:2508.17054},
+}
 ```
 
 And our excellent collaborators works contributed to this codebase also: