[skip ci] Add citations

CITATION.cff

@@ -0,0 +1,28 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+- family-names: "Scemama"
+  given-names: "Anthony"
+  orcid: "https://orcid.org/0000-0003-4955-7136"
+- family-names: "Posenitskiy"
+  given-names: "Evgeny"
+  orcid: "https://orcid.org/0000-0002-1623-0594"
+title: "TREX I/O library "
+version: 2.3.1
+date-released: 2023-04-26
+url: "https://github.com/TREX-CoE/trexio"
+preferred-citation:
+  type: article
+  authors:
+  - family-names: "Posenitskiy"
+    given-names: "Evgeny"
+  - family-names: "et al."
+    given-names: ""
+  doi: "10.1063/5.0148161"
+  journal: "The Journal of Chemical Physics"
+  month: 5
+  start: 174801 # First page number
+  title: "TREXIO: A file format and library for quantum chemistry"
+  issue: 17
+  volume: 158
+  year: 2023

README.md

@@ -208,6 +208,30 @@ For example, the tutorial covering TREXIO basics using benzene molecule as an ex
 [Documentation generated from TREXIO org-mode files.](https://trex-coe.github.io/trexio/)
 
 
+## Citation
+
+The journal article reference describing TREXIO can be cited as follows:
+
+```
+@article{10.1063/5.0148161,
+    author = {Posenitskiy, Evgeny and Chilkuri, Vijay Gopal and Ammar, Abdallah and Hapka, Michał and Pernal, Katarzyna and Shinde, Ravindra and Landinez Borda, Edgar Josué and Filippi, Claudia and Nakano, Kosuke and Kohulák, Otto and Sorella, Sandro and de Oliveira Castro, Pablo and Jalby, William and Ríos, Pablo López and Alavi, Ali and Scemama, Anthony},
+    title = "{TREXIO: A file format and library for quantum chemistry}",
+    journal = {The Journal of Chemical Physics},
+    volume = {158},
+    number = {17},
+    year = {2023},
+    month = {05},
+    issn = {0021-9606},
+    doi = {10.1063/5.0148161},
+    url = {https://doi.org/10.1063/5.0148161},
+    note = {174801},
+    eprint = {https://pubs.aip.org/aip/jcp/article-pdf/doi/10.1063/5.0148161/17355866/174801\_1\_5.0148161.pdf},
+}
+```
+
+Journal paper: [![doi](https://img.shields.io/badge/doi-10.1063/5.0148161-5077AB.svg)](https://doi.org/10.1063/5.0148161)
+ArXiv paper: [![arXiv](https://img.shields.io/badge/arXiv-2302.14793-b31b1b.svg)](https://arxiv.org/abs/2302.14793)
+
 ### Miscellaneous
 
 Note: The code should be compliant with the C99