docs: add citation info

docs/citing.md

@@ -1,5 +1,14 @@
 # Citing PolarToolkit
 
+This is research software made by scientists. Citations help us justify the effort that goes into building and maintaining this project.
+
+If you used `PolarToolkit` in your research, please consider citing our paper:
+
 ```{warning}
-Citation info still to come ...
+Journal of Open Source Software (JOSS) paper still in review ...
 ```
+
+This is an open-access publication.
+The paper and the associated software review can be freely accessed at: https://joss.theoj.org/papers/b3964f290fcd03c7706ef1973bcdf702
+
+If you would like to cite the specific version you used, which can improve reproducibility and let users know the state of the software at the time of your analysis, please use the version-specific citation and DOI (available from [Zenodo](https://zenodo.org/doi/10.5281/zenodo.7059091)).