Add CITATION file

Author: aglaws

CITATION.cff

@@ -0,0 +1,16 @@
+cff-version: 1.0.0
+message: "If you use this software, please cite it as below."
+authors:
+- family-names: "Harrison-Atlas"
+  given-names: "Dylan"
+- family-names: "Glaws"
+  given-names: "Andrew"
+- family-names: "King"
+  given-names: "Ryan"
+- family-names: "Lantz"
+  given-names: "Eric"
+title: "Wind Plant Graph Neural Network (WPGNN) and Plant Layout Generator (PLayGen)"
+version: 1.0.0
+doi: 10.11578/dc.20220509.2
+date-released: 2022-05-05
+url: "https://github.com/NREL/WPGNN"