Add release checklist

.github/ISSUE_TEMPLATE/release_checklist.md

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+---
+name: Release checklist
+about: Checklist to make a release
+title: ''
+labels: 'maintenance'
+assignees: ''
+
+---
+
+# CADET-Python Release Checklist
+
+CADET-Python follows the semantic versioning system described at [semver.org](https://semver.org/).
+
+CADET-Python is released direcntly from the master branch and deployed to PyPi via a GitHub workflow automatically, and to conda-forge semi-automatically.
+
+The following checklist describes the steps to execute sequentially for creating a new release.
+
+---
+
+## Preparation
+
+- [ ] Create a version bump commit `Bump version to vX.X.X`:
+  - Update the version number in 
+  - `__init__.py`
+  - `zenodo.json` (two places), `cadet.hpp` and 
+
+---
+
+## Creating the release on GitHub
+
+- [ ] Go to [GitHub Releases](https://github.com/cadet/CADET-Core/releases/new):
+  - Set the release branch as the target
+  - Specify the tag `vX.X.X` according to semantic versioning
+  - Add release notes with sections for Added, Fixed, Changed, and Updated
+  - Publish the release.
+- [ ] Check deployment on PyPi via the CI and the [PyPi CADET-Python website](https://pypi.org/project/CADET-Python/)
+- [ ] Verify Zenodo archiving:
+  - Confirm that a version-specific DOI was created
+  - Ensure that the source code and associated files are archived
+  - Note that the [concept DOI](https://doi.org/10.5281/zenodo.14132721) remains constant
+
+## Deployment on pypi
+
+- [ ] Check if the GitHub action with workflow file `python-publish.yml` ran successfully, fix if required.
+
+## Deployment on conda-forge
+
+- [ ] Go to your fork of [cadet-feedstock](https://github.com/conda-forge/cadet-python-feedstock) or create one if it does not exist
+- [ ] Create a new branch on your fork and change the file `recipe/meta.yaml`:
+  - install openSSL
+  - Generate the SHA256 key (replace `{{ version }}` with the semantic version number):  
+    ```bash
+    curl -sL https://github.com/cadet/CADET-Python/archive/refs/tags/v{{ version }}.tar.gz | openssl sha256
+    ```
+  - Update the version number and SHA256 key
+  - Set the build number to zero (`build: number: 0`)
+- [ ] Open a PR onto the `main` branch of `conda-forge/cadet-feedstock`, and complete the automatically generated checklist
+  - Note: to check if the license file is included, check the tarball (`https://github.com/cadet/CADET-Python/archive/refs/tags/v{{ version }}.tar.gz`) if the License file is in the location specified in the meta.yml in the variable `license_file`
+- [ ] Wait for the automatic checks to pass
+- [ ] Merge the pull request to trigger the conda-forge release
+- [ ] Double check if the new version of cadet-python is on conda-forge
+
+---
+
+## Follow-up
+- [ ] If this release checklist was updated, add these changes to the corresponding issue template