Screenshots would be nice I suppose, yeah. A walkthrough/instructions are sort of included in the app in the Start screen, at least enough to get stuff enabled. I think the keyboard UI is pretty easy to understand, and the buttons are large and there is no wasted space which is nice for accessibility. At this time there aren't any plans to publish it on F-Droid. However, Accrescent is the recommended way to get it as Accrescent provides automatic updates (which can be turned off if you'd prefer) and has higher security than GitHub and F-Droid. It's available on GitHub releases too.
There! I added a screenshot of the keyboard UI at the bottom of the README.md. There isn't really anything else to screenshot other than maybe the ACTION_RECOGNIZE_SPEECH activity but it's basically the same but floating and with only the mic button.