TL: added citation file and link to zenodo release (#6)

CITATION.cff

@@ -0,0 +1,29 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+
+abstract: "Generation of Q-coefficients for Spectral Deferred Corrections (and other time-integration methods ...)"
+authors: 
+  - family-names: Speck
+    given-names: Robert
+    orcid: https://orcid.org/0000-0002-3879-1210
+    affiliation: "Jülich Supercomputing Centre, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany"
+  - family-names: Lunet
+    given-names: Thibaut
+    orcid: https://orcid.org/0000-0003-1745-0780
+    affiliation: "Hamburg University of Technology, Institute of Mathematics, 21073 Hamburg, Germany"
+  - family-names: Baumann
+    given-names: Thomas
+    orcid: https://orcid.org/0000-0002-4676-7659
+    affiliation: "Jülich Supercomputing Centre, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany"
+
+version: 0.1.0
+doi: 10.5281/zenodo.11956479
+date-released: 2024-06-17
+keywords: 
+  - "time integration"
+  - "spectral deferred corrections"
+  - collocation
+  - "Runge-Kutta"
+license: BSD-2-Clause
+repository-code: https://github.com/Parallel-in-Time/qmat
+title: "Parallel-in-Time/qmat"

README.md

@@ -65,6 +65,8 @@ c, b, A = genQCoeffs("ERK4")
 in particular the [**step by step tutorials**](https://qmat.readthedocs.io/en/latest/notebooks.html)_
 
 
+Cite this package : [![DOI](https://zenodo.org/badge/804826743.svg)](https://zenodo.org/doi/10.5281/zenodo.11956478)
+
 For any contribution, please checkout out (very cool) [Contribution Guidelines](https://qmat.readthedocs.io/en/latest/contributing.html)
 
 ## Links