add new citation file

CITATION.bib

@@ -1,10 +1,11 @@
-@Article{gmd-2021-301,
+@Article{gmd-15-3161-2022,
 AUTHOR = {M\"uller, S. and Sch\"uler, L. and Zech, A. and He{\ss}e, F.},
-TITLE = {GSTools v1.3: A toolbox for geostatistical modelling in Python},
-JOURNAL = {Geoscientific Model Development Discussions},
-VOLUME = {2021},
-YEAR = {2021},
-PAGES = {1--33},
-URL = {https://gmd.copernicus.org/preprints/gmd-2021-301/},
-DOI = {10.5194/gmd-2021-301}
+TITLE = {\texttt{GSTools} v1.3: a toolbox for geostatistical modelling in Python},
+JOURNAL = {Geoscientific Model Development},
+VOLUME = {15},
+YEAR = {2022},
+NUMBER = {7},
+PAGES = {3161--3182},
+URL = {https://gmd.copernicus.org/articles/15/3161/2022/},
+DOI = {10.5194/gmd-15-3161-2022}
 }