sudo apt install apt-transport-https
wget -O - https://packages.gummi.app/pubkey | sudo apt-key add -
echo "deb [arch=$( dpkg --print-architecture )] https://packages.gummi.app/ubuntu/$(lsb_release -c -s)/ /" | sudo tee /etc/apt/sources.list.d/gummi.list
sudo apt update
sudo apt install gummi