The documentation is built by MkDocs. For full documentation visit mkdocs.org.
It's perfectly acceptable to just edit Markdown files on Github and submitting pull requests directly from there. If you feel unsure if your syntax is correct, it's pretty easy to run the site locally though, see below.
With Docker, it's a matter of simply docker-compose up.
Without Docker, you'll have to install the Python dependencies. Run pip install -r requirements.txt and then start the local server with mkdocs serve.
In both cases afterwards the site will be served from localhost:8000
Jenkins deploys changes automatically when merging to master.