Added a CITATION.cff file.

CITATION.cff

+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+- family-names: "Gamelin"
+  given-names: "Alexis"
+- family-names: "Foosang"
+  given-names: "Watanyu"
+- family-names: "Yamomoto"
+  given-names: "Naoto"
+- family-names: "Gubaidulin"
+  given-names: "Vadim"
+- family-names: "Nagaoka"
+  given-names: "Ryutaro"
+
+title: "mbtrack2"
+version: 0.8.0
+doi: https://doi.org/10.5281/zenodo.14418989
+date-released: 2024-12-16
+url: "https://gitlab.synchrotron-soleil.fr/PA/collective-effects/mbtrack2"