uner: add citation reference

universal_ner.py

@@ -4,6 +4,14 @@ import datasets
 
 
 _CITATION = r"""\
+@misc{mayhew2023universal,
+      title={Universal NER: A Gold-Standard Multilingual Named Entity Recognition Benchmark}, 
+      author={Stephen Mayhew and Terra Blevins and Shuheng Liu and Marek Šuppa and Hila Gonen and Joseph Marvin Imperial and Börje F. Karlsson and Peiqin Lin and Nikola Ljubešić and LJ Miranda and Barbara Plank and Arij Riabi and Yuval Pinter},
+      year={2023},
+      eprint={2311.09122},
+      archivePrefix={arXiv},
+      primaryClass={cs.CL}
+}
 """  # noqa: W605
 
 _DESCRIPTION = """\