In general, Linux programs are installed using a package manager such as Update Manager, Software Center, or Synaptic to fetch software from various repositories. Each one has slightly different ways of telling it where to look for software packages. It is also possible to use commands in a terminal to set it up and fetch it.

For those who are new to setting up package managers for Linux, instructions are in this document on Setting up Repositories to download SIL Software.

For those comfortable with it, the repository is packages.sil.org. There are some instructions (including the GPG key) at the SIL Linux Package Repository, but the relevant apt lines are:

deb http://packages.sil.org/ubuntu xenial main (for stable releases)

deb http://packages.sil.org/ubuntu xenial-experimental main (for beta releases)