A lot of resources (like logos, images, wallpaper, Joomla templates, slides) are also available, with sources, on a dedicated repository of Dolibarr GitHub. You can navigated into directories according to what you are looking for. All resources on this repository are provided under licence CC-By-SA. So you can use, modify and redistribute them even for a commercial usage..
To go onto the Github dedicated to Dolibarr resources: https://github.com/Dolibarr/foundation
It you are looking for documentation, take a look at this dedicated page