Work in progress, contributing with bug reports on the GitHub issues page is appreciated :)
If you don't already have the activitywatch python client library, install with
pip3 install pip3 install git+git@github.com:ActivityWatch/aw-client.git
Make sure that you have some vim runtimepath manager set up (such as Pathogen or Vundle)
Then simply clone this repository to the bundle folder in your vim config folder (usually ~/.vim/bundle or ~/.config/nvim/bundle for neovim)