This is basically a way to create menus and submenus for recurrent utilities. You can use a rofi or dmenu frontend. Once you bind it a key shortcut, rofi/dmenu will come up asking you what to do.
Right now I can directly access my favorite websites, open my favorite programs, do web search (and also switch web engine), all without touching the browser directly. The idea is to group a lot of things in a lightweight script, and have a keyboard-only interaction with no extra extensions or programs.
I agree that the README is a little poor right now, and screenshots/gifs would also help on this regard. I'll start working on it pretty soon.
It might be a good idea to add screenshots or a gif or something to the README, and I see they've realized that.
https://github.com/40ants/cl-bitbar
It is a library to write plugins for https://getbitbar.com