Add template CFF

Equivalent to the citation file added in carpentries/workbench-template-md#42

CITATION.cff

@@ -0,0 +1,22 @@
+# This template CITATION.cff file was generated with cffinit.
+# Visit https://bit.ly/cffinit to replace its contents
+# with information about your lesson.
+# Remember to update this file periodically, 
+# ensuring that the author list and other fields remain accurate.
+
+cff-version: 1.2.0
+title: FIXME
+message: >-
+  Please cite this lesson using the information in this file
+  when you refer to it in publications, and/or if you
+  re-use, adapt, or expand on the content in your own
+  training material.
+type: dataset
+authors:
+  - given-names: FIXME
+    family-names: FIXME
+abstract: >-
+  FIXME Replace this with a short abstract describing the
+  lesson, e.g. its target audience and main intended
+  learning objectives.
+license: CC-BY-4.0