Add publication DOI to README

README.md

@@ -34,7 +34,8 @@ installed package directory, or opened with:
 ## Bibliography
 
 P. Virtanen, "Numerical saddle point finding for diffusive superconductor actions",
-https://arxiv.org/abs/2406.19894 (2024).
+[Phys. Rev. B 111, 024510 (2025)](https://doi.org/10.1103/PhysRevB.111.024510),
+[arXiv:2406.19894](https://arxiv.org/abs/2406.19894).
 
 ## Acknowledgments