The documentation is in form of a readme, written in markdown.
View it online
here or by checking out the code and looking at README.md.
Quick reference:
- Activate overlay to switch windows: Alt + KeyAboveTab
- Navigate overlay: with the mouse, with the cursor keys, with tab
- Supports filtering: in the overlay, start typing out a work and it should filter the windows whose titles match that word
Have fun using it!