Merge pull request #79 from mbakker7/citation

add citation file

CITATION.cff

@@ -0,0 +1,25 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+ - family-names: "Bakker"
+ given-names: "Mark"
+ orcid: "https://orcid.org/0000-0002-5629-2861"
+title: "TimML"
+url: "https://github.com/mbakker7/timml"
+
+preferred-citation:
+ type: article
+ authors:
+ - family-names: "Bakker"
+ given-names: "Mark"
+ orcid: "https://orcid.org/0000-0002-5629-2861"
+ - family-names: "Strack" 
+ given-names: "Otto D.L."
+ doi: "10.1016/S0022-1694(02)00319-0"
+ journal: "Journal of Hydrology"
+ title: "Analytic elements for multiaquifer flow"
+ volume: 271
+ number: 1
+ start: 119
+ end: 129
+ year: 2003