Manage your system's Personal Package Archives (PPA) repository sources.
Repo is available from via AppCenter for elementary OS.
You can install Repo by compiling it from source.
Ensure you have these dependencies installed beforehand:
mesonvalaglib-2.0gobject-2.0gtk+-3.0>= 3.18gee-0.8granite>= 0.5.0software-properties-common
Run make build in the project's root folder.
Run make install