added CITATION.cff file (#783)

Author: sugatoray

CITATION.cff

@@ -0,0 +1,17 @@
+# file: CITATION.cff
+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+- family-names: "Yadan"
+  given-names: "Omry"
+  orcid: "https://orcid.org/0000-0002-1871-7216"
+- family-names: "Sommer-Simpson"
+  given-names: "Jasha"
+  orcid: "https://orcid.org/0000-0002-1397-6454"
+- family-names: "Delalleau"
+  given-names: "Olivier"
+  orcid: "https://orcid.org/0000-0002-0610-7226"
+title: "omegaconf"
+#doi: 10.5281/zenodo.1234
+date-released: 2019-11-19
+url: "https://github.com/omry/omegaconf"