Add BibTeX citation information to README (#47)

* Add BibTeX citation information ot README

* Add link to pre-print

README.md

@@ -44,6 +44,19 @@ print_z_state_probabilities(ρ)
 
 For a more comprehensive introduction see the [package documentation](https://lanl-ansi.github.io/QuantumAnnealing.jl/stable/).
 
+# Citation
+If QuantumAnnealing.jl proves useful in your work, please consider citing it using the following BibTeX citation for the pre-print, available [here](https://arxiv.org/abs/2404.14501):
+
+```
+@misc{morrell2024quantumannealing,
+      title={QuantumAnnealing: A Julia Package for Simulating Dynamics of Transverse Field Ising Models}, 
+      author={Zachary Morrell and Marc Vuffray and Sidhant Misra and Carleton Coffrin},
+      year={2024},
+      eprint={2404.14501},
+      archivePrefix={arXiv},
+      primaryClass={quant-ph}
+}
+```
 
 # License
 This software is provided under a BSD-ish license with a "modifications must be indicated" clause.  See the `LICENSE.md` file for the full text. This package is part of the Hybrid Quantum-Classical Computing suite, known internally as LA-CC-16-032.