add CITATION.cff (#117)

* add CITATION.cff

* remove nicolas schuck from CITATION.cff

* add more keywords to CITATION.cff

CITATION.cff

@@ -0,0 +1,33 @@
+# This CITATION.cff file was generated with cffinit.
+# Visit https://bit.ly/cffinit to generate yours today!
+
+cff-version: 1.2.0
+title: Version Control Book
+message: >-
+  If you use this software, please cite it using the
+  metadata from this file.
+type: software
+authors:
+  - given-names: Lennart
+    family-names: Wittkuhn
+    email: [email protected]
+    affiliation: University of Hamburg
+    orcid: 'https://orcid.org/0000-0003-2966-6888'
+  - given-names: Konrad
+    family-names: Pagenstedt
+    email: [email protected]
+    affiliation: University of Hamburg
+repository-code: 'https://github.com/lnnrtwttkhn/version-control-book'
+url: 'https://lennartwittkuhn.com/version-control-book/'
+abstract: >-
+  The Version Control Book is a comprehensive educational
+  resource for version control of code and data with Git for
+  scientists.
+keywords:
+  - version control
+  - git
+  - github
+  - reproducibility
+  - open science
+  - open eduational resources
+license: CC-BY-SA-4.0