add mention of the GMD breakup paper in README

Author: slayoo

README.md

@@ -51,9 +51,11 @@ The [`ThrustRTC`](https://open-atmos.github.io/PySDM/PySDM/backends/thrustRTC/th
   parallelisation model. 
 Using the ``GPU`` backend requires nVidia hardware and [CUDA driver](https://developer.nvidia.com/cuda-downloads).
 
-For an overview of PySDM features (and the preferred way to cite PySDM in papers), please refer to our JOSS paper:
+For an overview of PySDM features (and the preferred way to cite PySDM in papers), please refer to our JOSS papers:
 - [Bartman et al. 2022](https://doi.org/10.21105/joss.03219) (PySDM v1).
-- [de Jong et al. 2023](https://doi.org/10.21105/joss.04968) (PySDM v2).
+- [de Jong, Singer et al. 2023](https://doi.org/10.21105/joss.04968) (PySDM v2).
+  
+PySDM includes an extension of the SDM scheme to represent collisional breakup described in [de Jong, Mackay et al. 2023](10.5194/gmd-16-4193-2023).   
 For a list of talks and other materials on PySDM, see the [project wiki](https://github.com/open-atmos/PySDM/wiki).
 
 A [pdoc-generated](https://pdoc3.github.io/pdoc) documentation of PySDM public API is maintained at: [https://open-atmos.github.io/PySDM](https://open-atmos.github.io/PySDM)