docs: add paper link and bibtex citation

README.md

@@ -15,7 +15,7 @@ pipeline_tag: text-classification
 
 **R2-Router** intelligently routes each query to the optimal (LLM, token budget) pair, jointly optimizing accuracy and inference cost. Ranked **#1** on the [RouterArena](https://routerarena.github.io/) leaderboard.
 
-**Paper**: [R2-Router (arxiv)](https://arxiv.org/abs/TODO)
+**Paper**: [R2-Router (arxiv)](https://arxiv.org/abs/2602.02823)
 
 ## RouterArena Performance
 
@@ -191,11 +191,11 @@ checkpoints/
 ## Citation
 
 ```bibtex
-@article{r2router2026,
+@article{xue2026r2,
   title={R2-Router: A New Paradigm for LLM Routing with Reasoning},
-  author={TODO},
-  year={2026},
-  url={https://arxiv.org/abs/TODO}
+  author={Xue, Jiaqi and Lou, Qian and Xing, Jiarong and Huang, Heng},
+  journal={arXiv preprint arXiv:2602.02823},
+  year={2026}
 }
 ```