In-tree Sphinx example, with a directive linking docs having certain labels

How to build this

1. Install the deps

   pip install -r requirements.in -c requirements.txt
   

2. Run the build

   sphinx-build -b html -j auto -d ./build/doctrees -T -n -W --keep-going -E ./source/ ./build/
   

3. Open it

   xdg-open "$(pwd)"/build/index.html