If you are running old version of Shion OS (<1.1.2) before the official repository existed or you simply want to add the repository to another operating system it is fairly simple.
First you should install the GPG authentication key by running teh command below in a terminal:
cd /tmp && wget https://sourceforge.net/projects/shionos/files/repo/key/shion-public.deb.key.gpg/download -O shion-public.deb.key.gpg && sudo apt-key add /tmp/shion-public.deb.key.gpg
Now to add the APT source. Sources can be added a number of ways but the simplest is to run the command below:
sudo wget https://sourceforge.net/projects/shionos/files/repo/source%20lists/shion-os-1.list -O /etc/apt/sources.list.d/shion-os-1.list
You can also add the beta repository for bleading edge package updates:
sudo wget https://sourceforge.net/projects/shionos/files/repo/source%20lists/shion-os-1-beta.list -O /etc/apt/sources.list.d/shion-os-1-beta.list