In order to build the docs locally, you need to have the following installed:
For example, you may install these dependencies using pip:
pip install -U sphinx sphinx-rtd-theme
For other installation methods refer to the docs of the dependencies.
In archinstall/docs, run make html (or specify another target) to build locally. The build files will be in archinstall/docs/_build. Open _build/html/index.html with your browser to see your changes in action.