add: citation file

Author: koalamitice

CITATION.bib

@@ -0,0 +1,6 @@
+@article{eichhorn2025provideq,
+  title = {ProvideQ: A Quantum Optimization Toolbox},
+  author = {Eichhorn, Domenik and Poser, Nick and Schweikart, Maximilian and Schaefer, Ina},
+  journal = {arXiv preprint arXiv:2507.07649},
+  year = {2025}
+}