Add RobustPeriod reference to README

README.md

@@ -48,3 +48,4 @@ All the supported estimation algorithms can be used in the same manner as in the
 - [1] Hyndman, R.J., & Athanasopoulos, G. (2021) Forecasting: principles and practice, 3rd edition, OTexts: Melbourne, Australia. [OTexts.com/fpp3](https://otexts.com/fpp3). Accessed on 09-15-2024.
 - [2] Vlachos, M., Yu, P., & Castelli, V. (2005). On periodicity detection and Structural Periodic similarity. Proceedings of the 2005 SIAM International Conference on Data Mining. [doi.org/10.1137/1.9781611972757.40](https://doi.org/10.1137/1.9781611972757.40).
 - [3] Puech, T., Boussard, M., D'Amato, A., & Millerand, G. (2020). A fully automated periodicity detection in time series. In Advanced Analytics and Learning on Temporal Data: 4th ECML PKDD Workshop, AALTD 2019, Würzburg, Germany, September 20, 2019, Revised Selected Papers 4 (pp. 43-54). Springer International Publishing. [doi.org/10.1007/978-3-030-39098-3_4](https://doi.org/10.1007/978-3-030-39098-3_4).
+- [4] Wen, Q., He, K., Sun, L., Zhang, Y., Ke, M., & Xu, H. (2021, June). RobustPeriod: Robust time-frequency mining for multiple periodicity detection. In Proceedings of the 2021 international conference on management of data (pp. 2328-2337). [https://doi.org/10.1145/3448016.3452779](https://doi.org/10.1145/3448016.3452779).