I wanted to add Wiki/ToH entries for 'PowerCloud Systems' devices (CR3000, CR5000, and CAP324). They have been supported since LEDE release and will also be in 18.06, so I thought it'd be good to have a ToH entry for each. I'll see if I can figure out how to add just a device page at least.
I've never added a new ToH page, just edited the existing one, but it's still a wiki, you should be able to.
If that section is restricted and wouldn't let you create a new page -- create a new page following the device templates in the playground (there was a safer location to do that, forgot what it was) and PM the wiki/web-site team the link(s).
Apparently (from the looks of the what I read) the ToH is specially handled and the it's not so easily done; the pages have to follow a very specific format AIUI, and I could find the empty template for a page (the ToH section is designed so that you have to go through the ToH entry generator). It's all to do with preventing borking the ToH.
I'd take an existing device page as a template and follow that. Either something like WRT series if the same page is going to cover multiple devices or some simple device page if you're going to create an individual page per device.