🔧 requirements.in contains the direct dependencies

Now `requirements.in` contains the project's direct dependencies (i.e., top-level),
whereas the generated `requirements.txt` includes all dependencies (direct + indirect).

To add/update dependencies, use `requirements.in` as the source to build `requirements.txt`:

```shell
 # Edit requirements.in

 # Remove all installed dependencies
python -m pip freeze --exclude-editable | xargs python -m pip  uninstall -y

 # Install direct dependencies (and their dependencies)
python -m pip install -r requirements.in

 # Pin all dependencies in requirements.txt
 # ie. List all the dependencies (direct and indirect) in
 # requirements.txt with their  version number
python -m pip freeze > requirements.txt
````

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Author: ebouchut

requirements.in

@@ -0,0 +1,5 @@
+certifi==2024.7.4
+mkdocs==1.6.1
+mkdocs-htmlproofer-plugin==1.3.0
+mkdocs-material==9.5.49
+mkdocs-unused-files==0.2.0