add citation

CITATION.cff

@@ -0,0 +1,21 @@
+cff-version: 1.2.0
+message: "If you use OSMnx, please cite the preferred-citation below."
+title: "OSMnx Examples"
+abstract: "Gallery of OSMnx tutorials, usage examples, and feature demonstations."
+authors:
+- family-names: "Boeing"
+  given-names: "Geoff"
+  orcid: "https://orcid.org/0000-0003-1851-6411"
+  website: "https://geoffboeing.com"
+url: "https://osmnx.readthedocs.org"
+repository-code: "https://github.com/gboeing/osmnx-examples"
+preferred-citation:
+  type: report
+  title: "Modeling and Analyzing Urban Networks and Amenities with OSMnx"
+  authors:
+  - family-names: "Boeing"
+    given-names: "Geoff"
+    orcid: "https://orcid.org/0000-0003-1851-6411"
+    website: "https://geoffboeing.com"
+  year: 2024
+  url: "https://geoffboeing.com/publications/osmnx-paper/"