Add links to the JOSS paper (#965)

* Add the link to the JOSS doc in the README

* Add the CITATION.cff file

Author: EmilyBourne

CITATION.cff

@@ -0,0 +1,48 @@
+# Copyright (C) The DDC development team, see COPYRIGHT.md file
+#
+# SPDX-License-Identifier: MIT
+cff-version: "1.2.0"
+authors:
+- family-names: Padioleau
+  given-names: Thomas
+  orcid: "https://orcid.org/0000-0001-5496-0013"
+- family-names: Bigot
+  given-names: Julien
+  orcid: "https://orcid.org/0000-0002-0015-4304"
+- family-names: Bourne
+  given-names: Emily
+  orcid: "https://orcid.org/0000-0002-3469-2338"
+- family-names: Legouix
+  given-names: Baptiste
+  orcid: "https://orcid.org/0009-0006-7585-669X"
+doi: 10.5281/zenodo.17511922
+message: If you use this software, please cite our article in the
+  Journal of Open Source Software.
+preferred-citation:
+  authors:
+  - family-names: Padioleau
+    given-names: Thomas
+    orcid: "https://orcid.org/0000-0001-5496-0013"
+  - family-names: Bigot
+    given-names: Julien
+    orcid: "https://orcid.org/0000-0002-0015-4304"
+  - family-names: Bourne
+    given-names: Emily
+    orcid: "https://orcid.org/0000-0002-3469-2338"
+  - family-names: Legouix
+    given-names: Baptiste
+    orcid: "https://orcid.org/0009-0006-7585-669X"
+  date-published: 2025-11-06
+  doi: 10.21105/joss.09122
+  issn: 2475-9066
+  issue: 115
+  journal: Journal of Open Source Software
+  publisher:
+    name: Open Journals
+  start: 9122
+  title: "DDC: The Discrete Domain Computation library"
+  type: article
+  url: "https://joss.theoj.org/papers/10.21105/joss.09122"
+  volume: 10
+title: "DDC: The Discrete Domain Computation library"
+

README.md

@@ -11,6 +11,7 @@ SPDX-License-Identifier: MIT
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 [![Nightly early integration](https://github.com/CExA-project/ddc/actions/workflows/early_integration.yaml/badge.svg?event=schedule)](https://github.com/CExA-project/ddc/actions/workflows/early_integration.yaml)
 [![Pages](https://github.com/CExA-project/ddc/actions/workflows/pages.yaml/badge.svg)](https://github.com/CExA-project/ddc/actions/workflows/pages.yaml)
+[![DOI](https://joss.theoj.org/papers/10.21105/joss.09122/status.svg)](https://doi.org/10.21105/joss.09122)
 
 See <https://ddc.mdls.fr/>