Add citation for ZOSPy JOSS paper

README.md

@@ -9,7 +9,7 @@ It provides an easy-to-use interface to define and build eye models, and to perf
 2. Provide a collection of ready-to-use eye models, such as the Navarro model[^navarro], that can be customized at need;
 3. Provide an accessible interface to clinically relevant analyses with these models.
 
-All calculations are currently performed in OpticStudio through the [ZOSPy][zospy] library, but visisipy is designed in a modular fashion to allow for other backends in the future.
+All calculations are currently performed in OpticStudio through the [ZOSPy][zospy][^zospy] library, but visisipy is designed in a modular fashion to allow for other backends in the future.
 
 ## Contributing
 
@@ -145,3 +145,4 @@ built_model.lens_front.radius = 10.5
 [//]: # (References)
 [^navarro]: Escudero-Sanz, I., & Navarro, R. (1999). Off-axis aberrations of a wide-angle schematic eye model. JOSA A, 16(8), 1881–1891. https://doi.org/10.1364/JOSAA.16.001881
 [^rozema]: Rozema, J. J., Rodriguez, P., Navarro, R., & Tassignon, M.-J. (2016). SyntEyes: A Higher-Order Statistical Eye Model for Healthy Eyes. Investigative Ophthalmology & Visual Science, 57(2), 683–691. https://doi.org/10.1167/iovs.15-18067
+[^zospy]: Vught, L. van, Haasjes, C., & Beenakker, J.-W. M. (2024). ZOSPy: Optical ray tracing in Python through OpticStudio. Journal of Open Source Software, 9(96), 5756. https://doi.org/10.21105/joss.05756