chore: update README.md

Author: phumthep

README.md

@@ -85,3 +85,19 @@ This command installs the package in "editable" mode (-e) using pyproject.toml t
 ![overview_pownet](./joss_submission/overview_pownet.png)
 
 
+# Citing this software
+If you use PowNet 2.0 in your work, please cite the following article:
+
+@article{
+  Bunnak2025,
+  doi = {10.21105/joss.08035},
+  url = {https://doi.org/10.21105/joss.08035},
+  year = {2025},
+  publisher = {The Open Journal},
+  volume = {10},
+  number = {111},
+  pages = {8035},
+  author = {Bunnak, Phumthep and Eldardiry, Hisham and Pavičević, Matija and Feng, Jerry Zhuoer and Galelli, Stefano},
+  title = {PowNet 2.0: A production cost modeling framework for large-scale power systems},
+  journal = {Journal of Open Source Software}
+}