Akaunting documentation is not only for its core features but also for modules. The documentation of modules will be shown both on documentation site and embed into Akaunting itself.
As mentioned in the README file, the menu file contains the navigation structure of the documentation. You should add your module under its respective category.
After adding to menu, you should create a file under the respective folder. If there is no such a folder, feel free to create it. Screenshots can be placed into the _images folder.
Check out this commit as a live example.