Resolve "cleanup repo"

Closes #12 (closed)
Upload citation.cff

CITATION.cff

+# This CITATION.cff file was generated with cffinit.
+# Visit https://bit.ly/cffinit to generate yours today!
+
+cff-version: 1.2.0
+title: toarstats
+message: >-
+  If you use this software, please cite it using the
+  metadata from this file.
+type: software
+authors:
+- email: n.selke@fz-juelich.de
+  orcid: https://orcid.org/0000-0002-9954-2250
+  family-names: Selke
+  given-names: Niklas
+- email: m.schultz@fz-juelich.de
+  orcid: https://orcid.org/0000-0003-3455-774X
+  family-names: Schultz
+  given-names: Martin
+  affiliation: Forschungszentrum Jülich
+contact:
+- email: m.schultz@fz-juelich.de
+  orcid: https://orcid.org/0000-0003-3455-774X
+  family-names: Schultz
+  given-names: Martin
+  affiliation: Forschungszentrum Jülich
+repository-code: >-
+  https://gitlab.jsc.fz-juelich.de/esde/toar-public/toarstats
+license: MIT