cli/components/engine/docs/sources/static_files/README.md

Static files dir

Files you put in /sources/static_files/ will be copied to the web visible /_static/

Be careful not to override pre-existing static files from the template.

Generally, layout related files should go in the /theme directory.

If you want to add images to your particular documentation page. Just put them next to your .rst source file and reference them relatively.