The code for this software is hosted at https://github.com/voegelas/gimp-screenshot-grim-plugin.
Grab the latest version using the commands:
mkdir -p ~/.config/GIMP/3.0/plug-ins
git clone https://github.com/voegelas/gimp-screenshot-grim-plugin.git \
~/.config/GIMP/3.0/plug-ins/screenshot-grim
You can submit code changes by forking the repository, pushing your code changes to your clone, and then submitting a pull request.
In order to update the locale message catalogs, install gettext and run:
make locales