add CITATION.cff

CITATION.cff

@@ -0,0 +1,18 @@
+cff-version: 1.2.0
+title: "seedbank: easy management of seeds across RNGs"
+message: >-
+    If you use this software, please cite it using the
+    metadata from this file.
+type: software
+authors:
+    - given-names: Michael D.
+      family-names: Ekstrand
+      email: ekstrand@acm.org
+      orcid: "https://orcid.org/0000-0003-2467-0108"
+repository-code: "https://github.com/lenskit/seedbank"
+url: "https://seedbank.lenskit.org"
+keywords:
+    - random numbers
+license: MIT
+version: 0.1.3
+date-released: "2023-09-28"