You can edit any page by pressing `ESC` on your keyboard or by clicking the "Edit" button on the bottom-right side of your screen. You will be able to preview your changes by pressing `ESC` again or by clicking the "preview" button.
The YunoHost documentation is managed through a [git repository](https://github.com/YunoHost/doc). You can send pull-requests, and do not forget to report your issues.