Update README.md with DOI, Zenodo and CC0 badges.

README.md

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+[![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.14230901.svg)](https://doi.org/10.5281/zenodo.14230901) [![License: CC0-1.0](https://img.shields.io/badge/License-CC0_1.0-lightgrey.svg)](http://creativecommons.org/publicdomain/zero/1.0/)
+
 # Matters of Police Ordinances
 
 The file `polmat.ttl`contains a systematic taxonomy of more than 1.800 matters regulated by police ordinances (last revised: Oct 2021). It is a SKOS vocabulary encoded in ttl/"turtle" format.
@@ -11,3 +13,4 @@ Translations by:
 - Toomas Kotkas and Annemieke Romein (English)
 
 The taxonomy and other aspects of modeling police ordinances data are currently maintained and further developed by a "police ordinances community" (see this [wiki and repository](https://github.com/rhonda-org/PoliceOrdinances/wiki)).
+The taxonomy is published under CC0, but we will be happy if you give attribution when you use it.