We started working on one (using Googlecode wiki feature) but it ended with "startup guide" and lot or incomplete pages.
I hoped someone was interested enough to help us, but we were only two users working on it, and it finally ended as a dead project.
it had a navigation bar:
https://code.google.com/archive/p/usbloader-gui/wikis/SideNav.wiki
and three completed pages haha :
https://code.google.com/archive/p/usbloader-gui/wikis/Introduction.wiki
https://code.google.com/archive/p/usbloader-gui/wikis/Installation.wiki
https://code.google.com/archive/p/usbloader-gui/wikis/Changelog.wiki
other "work in progress" was done on a different googlecode project, as each edit on wiki increased the revision number of the loader :
https://code.google.com/archive/p/usbguiwikicolab/wikis
It used to contains pictures too, googlecode archive removed all the linked media.
We expected to explain how to setup, how to use, explain every settings and their uses, and do a reverse "setting" search, like a menu with many "how to xxxxx" -> set this setting, or "how to play gamecube" etc.
There were a start of "advanced game filtering guide" and other kind of pages and tuto.
It took too much time (that we spent elsewhere... probably here repeating the same answers that we could have written to the guide directly ahaha).
If someone is interested in writing the guide, let me know. but it will probably require a good knowledge of the loader, and also a good guide writing skill (writing info in chronological order, etc.).
The guide has to be written with "complete non-tech end users" in mind. all ages and new to the wii should be able to follow and understand what they are doing.
a guide telling "press A and it's done" is not good way to teach how to use a program.