Citable code (#238)

Add CITATION.cff, note DOIs in Readme

CITATION.cff

@@ -0,0 +1,66 @@
+cff-version: 1.2.0
+title: "RTE+RRTMGP"
+authors:
+  - family-names: Pincus
+    given-names: Robert
+    orcid: "https://orcid.org/0000-0002-0016-3470"
+  - family-names: Iacono
+    given-names: Michael J. 
+    orcid: "https://orcid.org/0000-0002-9578-0649"
+  - family-names: Alexeev
+    given-names: Dmitry 
+    orcid: "https://orcid.org/0000-0002-6425-2181"
+  - family-names: Adamidis
+    given-names: Panos
+  - family-names: Hillman
+    given-names: Benjamin R.
+    orcid: "https://orcid.org/0000-0002-9264-9872"
+  - family-names: Norman
+    given-names: Matthew
+    orcid: "https://orcid.org/0000-0003-4764-3348"
+  - family-names: Pfister
+    given-names: Erik 
+    orcid: "http://orcid.org/0009-0002-2688-138X"
+  - family-names: Polonsky
+    given-names: Igor N.
+  - family-names: Romero
+    given-names: Nicols A. 
+  - family-names: Wehe
+    given-names: Andre
+type: software
+repository-code: "https://github.com/earth-system-radiaton/rte-rrtmgp"
+license: BSD-3-Clause
+date-released: "2023-05-30"
+version: 1.7
+
+abstract: "RTE+RRTMGP is a set of codes for computing radiative fluxes in planetary atmospheres. 
+  RRTMGP uses a k-distribution to provide an optical description (absorption and possibly Rayleigh optical depth) of the gaseous atmosphere, along with the relevant source functions, on a pre-determined spectral grid given temperatures, pressures, and gas concentration. RTE computes fluxes given spectrally-resolved optical descriptions and source functions. The fluxes are normally summarized or reduced via a user extensible class."
+identifiers:
+  - description: "All versions"
+    type: doi
+    value: 10.5281/zenodo.3403172
+keywords:
+  - "RTE+RRTMGP"
+  - "atmospheric radiation"
+  - "radiative transfer"
+  - "climate model"
+  - research
+message: "If you use this software, please cite it using these metadata."
+
+references:
+  - authors:
+    - family-names: Pincus
+      given-names: Robert
+    - family-names: Mlawer
+      given-names: Eli J.
+    - family-names: Delamere
+      given-names: Jennifer S.
+    doi: 10.1029/2019MS001621
+    journal: "Journal of Advances in Modeling Earth Systems"
+    scope: "This paper describes the design, concepts, and version 1.0 of the software"
+    title: "Balancing Accuracy, Efficiency, and Flexibility in Radiation Calculations for Dynamical Models"
+    type: article
+    volume: 11
+    number: 10
+    pages: 3074-3089
+    year: 2019

README.md

@@ -17,6 +17,7 @@ RTE computes fluxes given spectrally-resolved optical descriptions and source fu
 
 
 ## Building the libraries, examples, and unit-testing codes.
+RTE+RRTMGP has an ad hoc homemade build system that can be invoked as follows: 
 
 1. Set environment variables `FC` (the Fortran 2003 compiler) and `FCFLAGS` (compiler flags). Examples are provided in the `Compiler-flags.md` file.
 2. Set environment variables `RRTMGP_ROOT` to the top-level RTE+RRTMGP directory and `RTE_KERNELS` to `accel` if you want the OpenACC/OpenMP kernels rather than the default.
@@ -27,6 +28,22 @@ RTE computes fluxes given spectrally-resolved optical descriptions and source fu
 7. Evaluating the results of the tests requires `Python` and the packages described in `environment.yml`. Comparisons can be made with `make check` in the top level directory. 
 8. `make` invoked without a target in the top level attempts all three steps.
 
+See also the `autoconf` branch for a Gnu autotools build system. 
+
 ## Examples
 
 Two examples are provided in `examples/`, one for clear skies and one including clouds. Directory `tests/` contains regression testing (e.g. to ensure that answers are independent of orientation) and unit testing (to be sure all the code paths are tested). See the README file and codes in each directory for further information.
+
+## Citing the code 
+
+Code releases are archived at Zenodo. All releases are available at 
+[![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3403172.svg)](https://doi.org/10.5281/zenodo.3403172). 
+The current release is available at: [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.7521518.svg)](https://doi.org/10.5281/zenodo.7521518)
+
+Please cite the code using these DOIs and the information in the `CITATION.cff` file in addition to the reference [paper](https://doi.org/10.1029/2019MS001621)
+
+## Acknowledgements
+
+The development of RTE+RRTMGP has been funded in the US by the Office of Naval Research, NASA, NOAA, and the Department of Energy. We 
+are grateful for contributions from a range of collaborators at institutions including the Swiss Supercomputing Center, 
+the German Climate Computing Center, and Nvidia.