Add JOSS citation (#18)

CITATION.cff

@@ -0,0 +1,56 @@
+cff-version: "1.2.0"
+authors:
+- family-names: Hellemo
+  given-names: Lars
+  orcid: "https://orcid.org/0000-0001-5958-9794"
+- family-names: Bødal
+  given-names: Espen Flo
+  orcid: "https://orcid.org/0000-0001-6970-9315"
+- family-names: Holm
+  given-names: Sigmund Eggen
+  orcid: "https://orcid.org/0009-0007-1782-6326"
+- family-names: Pinel
+  given-names: Dimitri
+  orcid: "https://orcid.org/0000-0001-9393-0036"
+- family-names: Straus
+  given-names: Julian
+  orcid: "https://orcid.org/0000-0001-8622-1936"
+contact:
+- family-names: Hellemo
+  given-names: Lars
+  orcid: "https://orcid.org/0000-0001-5958-9794"
+doi: 10.5281/zenodo.11164518
+message: If you use this software, please cite our article in the
+  Journal of Open Source Software.
+preferred-citation:
+  authors:
+  - family-names: Hellemo
+    given-names: Lars
+    orcid: "https://orcid.org/0000-0001-5958-9794"
+  - family-names: Bødal
+    given-names: Espen Flo
+    orcid: "https://orcid.org/0000-0001-6970-9315"
+  - family-names: Holm
+    given-names: Sigmund Eggen
+    orcid: "https://orcid.org/0009-0007-1782-6326"
+  - family-names: Pinel
+    given-names: Dimitri
+    orcid: "https://orcid.org/0000-0001-9393-0036"
+  - family-names: Straus
+    given-names: Julian
+    orcid: "https://orcid.org/0000-0001-8622-1936"
+  date-published: 2024-05-17
+  doi: 10.21105/joss.06619
+  issn: 2475-9066
+  issue: 97
+  journal: Journal of Open Source Software
+  publisher:
+    name: Open Journals
+  start: 6619
+  title: "EnergyModelsX: Flexible Energy Systems Modelling with Multiple
+    Dispatch"
+  type: article
+  url: "https://joss.theoj.org/papers/10.21105/joss.06619"
+  volume: 9
+title: "EnergyModelsX: Flexible Energy Systems Modelling with Multiple
+  Dispatch"

README.md

@@ -1,5 +1,6 @@
 # EnergyModelsRenewableProducers
 
+[![DOI](https://joss.theoj.org/papers/10.21105/joss.06619/status.svg)](https://doi.org/10.21105/joss.06619)
 [![Build Status](https://github.com/EnergyModelsX/EnergyModelsRenewableProducers.jl/workflows/CI/badge.svg)](https://github.com/EnergyModelsX/EnergyModelsRenewableProducers.jl/actions?query=workflow%3ACI)
 [![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://energymodelsx.github.io/EnergyModelsRenewableProducers.jl/stable/)
 [![In Development](https://img.shields.io/badge/docs-dev-blue.svg)](https://energymodelsx.github.io/EnergyModelsRenewableProducers.jl/dev/)
@@ -15,7 +16,21 @@ The examples are minimum working examples highlighting the individual new nodes
 
 ## Cite
 
-If you find `EnergyModelsRenewableProducers` useful in your work, we kindly request that you cite the following publication:
+If you find `EnergyModelsRenewableProducers` useful in your work, we kindly request that you cite the following [publication](https://doi.org/10.21105/joss.06619):
+
+```bibtex
+@article{hellemo2024energymodelsx,
+  title={EnergyModelsX: Flexible Energy Systems Modelling with Multiple Dispatch},
+  author={Hellemo, Lars and B{\o}dal, Espen Flo and Holm, Sigmund Eggen and Pinel, Dimitri and Straus, Julian},
+  journal={Journal of Open Source Software},
+  volume={9},
+  number={97},
+  pages={6619},
+  year={2024}
+}
+```
+
+For earlier work, see our [paper in Applied Energy](https://www.sciencedirect.com/science/article/pii/S0306261923018482):
 
 ```bibtex
 @article{boedal_2024,