Update README.md

README.md

@@ -49,4 +49,9 @@ https://www.hft-stuttgart.de/p/thunyathep-santhanavanich
 |------------------------------------------------------------------|-------------------------------------|
 | 3D Data Container and Tiles API Pilot Summary Engineering Report | http://docs.ogc.org/per/20-031.html |
 | Interoperable Simulation and Gaming Sprint Engineering Report    | http://docs.ogc.org/per/20-087.html |
-| Steinbeis Demo                                                   | https://steinbeis-3dps.eu |
\ No newline at end of file
+| Steinbeis Demo                                                   | https://steinbeis-3dps.eu |
+
+## Citation
+```
+Santhanavanich, Thunyathep. (2021). OGC 3D GeoVolumes API. Zenodo. https://doi.org/10.5281/zenodo.5731579
+```