adding citation file

Signed-off-by: vsoch <[email protected]>

Author: vsoch

CITATION.cff

@@ -0,0 +1,10 @@
+cff-version: 1.1.0
+message: "If you use this software, please cite it as below."
+authors:
+  - family-names: Sochat
+    given-names: Vanessa
+    orcid: https://orcid.org/0000-0002-4387-3819
+title: "Singularity Compose: Orchestration for Singularity Instances"
+version: 0.1.0
+doi: 10.21105/joss.01578
+date-released: 2019-08-26