update readme

Author: zhenfeizhang

README.md

@@ -9,3 +9,15 @@ cargo bench [--features=parallel]
 ```
 
 ![](bench.png)
+
+# Citation
+
+```bibtex
+@misc{cryptoeprint:2022/694,
+      author = {Nils Fleischhacker and Mark Simkin and Zhenfei Zhang},
+      title = {Squirrel: Efficient Synchronized Multi-Signatures from Lattices},
+      howpublished = {ACM CCS}
+      year = {2022},
+      url = {https://eprint.iacr.org/2022/694}
+}
+```