add github citation (#67)

add github citation

CITATION.cff

@@ -0,0 +1,26 @@
+cff-version: "1.2.0"
+message: If you use this software, please cite our article in Statistics and Computing.
+preferred-citation:
+  type: article
+  authors:
+  - family-names: Kallioinen
+    given-names: Noa
+    orcid: "https://orcid.org/0000-0003-1586-8382"
+  - family-names: Paananen
+    given-names: Topi
+    orcid: "https://orcid.org/0000-0002-6542-407X"
+  - family-names: Bürkner
+    given-names: Paul-Christian
+    orcid: "https://orcid.org/0000-0001-5765-8995"
+  - family-names: Vehtari
+    given-names: Aki
+    orcid: "https://orcid.org/0000-0003-2164-9469"
+  year: 2023
+  doi: 10.1007/s11222-023-10366-5
+  pages: 57
+  journal: Statistics and Computing
+  publisher:
+    name: Springer Nature
+  volume: 34
+  title: "Detecting and diagnosing prior and likelihood sensitivity with power-scaling"
+  url: "https://link.springer.com/article/10.1007/s11222-023-10366-5"