docs: add doi to citation.cff and badge to readme (#66)

Author: afuetterer

CITATION.cff

@@ -1,5 +1,5 @@
 cff-version: 1.2.0
-message: "If you use this software, please cite it as below."
+message: "If you use python-re3data, please cite it as below."
 type: software
 authors:
 - family-names: Fütterer
@@ -16,5 +16,9 @@ keywords:
 - re3data
 - repositories
 - research data
+identifiers:
+- description: This is the collection of archived snapshots of all versions of python-re3data
+  type: doi
+  value: 10.5281/zenodo.11264510
 version: 0.2.0
 date-released: 2024-05-23

README.md

@@ -9,7 +9,7 @@
 | :---------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | __Docs__    | [![docs][docs-badge]][docs-workflow]                                                                                                                                                                                                                                           |
 | __Package__ | [![pypi-status][status-badge]][pypi-url] [![pypi-version][pypi-version-badge]][pypi-url] [![pypi-python-versions][pypi-python-versions-badge]][pypi-url] [![all-downloads][all-downloads-badge]][pepy-tech-url] [![monthly-downloads][monthly-downloads-badge]][pepy-tech-url] |
-| __Meta__    | [![OpenSSF Scorecard][scorecard-badge]][scorecard-url] [![hatch][hatch-badge]][hatch] [![ruff][ruff-badge]][ruff] [![mypy][mypy-badge]][mypy] [![License][license-badge]][license-url]                                                                                         |
+| __Meta__    | [![doi][doi-badge]][doi-url] [![OpenSSF Scorecard][scorecard-badge]][scorecard-url] [![hatch][hatch-badge]][hatch] [![ruff][ruff-badge]][ruff] [![mypy][mypy-badge]][mypy] [![License][license-badge]][license-url]                                                            |
 
 `python-re3data` is a Python library that simplifies interacting with the [re3data](https://www.re3data.org) (Registry
 of Research Data Repositories) [REST API](https://www.re3data.org/api/doc), allowing you to easily retrieve and process
@@ -98,6 +98,8 @@ There are a couple of similar projects available on GitHub, e.g. via the topic
 [docs-badge]: https://github.com/afuetterer/python-re3data/actions/workflows/docs.yml/badge.svg
 [docs-url]: https://afuetterer.github.io/python-re3data
 [docs-workflow]: https://github.com/afuetterer/python-re3data/actions/workflows/docs.yml
+[doi-badge]: https://zenodo.org/badge/DOI/10.5281/zenodo.11264510.svg
+[doi-url]: https://doi.org/10.5281/zenodo.11264510
 [hatch]: https://github.com/pypa/hatch
 [hatch-badge]: https://img.shields.io/badge/%F0%9F%A5%9A-Hatch-4051b5.svg
 [license-badge]: https://img.shields.io/badge/license-MIT-blue.svg