Update README.md

Add a comma

README.md

@@ -111,7 +111,7 @@ Phys. Rev. Lett. **131**, 146101 (2023).
 Journal of Physics: Condensed Matter **36**, 245901 (2024).
 
 [14] Keke Song, Rui Zhao, Jiahui Liu, Yanzhou Wang, Eric Lindgren, Yong Wang, Shunda Chen, Ke Xu, Ting Liang, Penghua Ying, Nan Xu, Zhiqiang Zhao, Jiuyang Shi, Junjie Wang, Shuang Lyu, Zezhu Zeng, Shirong Liang, Haikuan Dong, Ligang Sun, Yue Chen, Zhuhua Zhang, Wanlin Guo, Ping Qian, Jian Sun, Paul Erhart, Tapio Ala-Nissila, Yanjing Su, Zheyong Fan,
-[General-purpose machine-learned potential for 16 elemental metals and their alloys](https://doi.org/10.1038/s41467-024-54554-x)
+[General-purpose machine-learned potential for 16 elemental metals and their alloys](https://doi.org/10.1038/s41467-024-54554-x),
 Nature Communications **15**, 10208 (2024).
 
 [15] Nan Xu, Petter Rosander, Christian Schäfer, Eric Lindgren, Nicklas Österbacka, Mandi Fang, Wei Chen, Yi He, Zheyong Fan, Paul Erhart,