This README fell too far out of date and is undergoing resurrection. Meanwhile, these bits are still relevant ...
If you just want to use the software without modifying/building it, you can download a pre-built package from the github releases page or the corresponding repo at JLab. Builds on JLab machines are also available, see the general software wiki for setting up your environment to use them.
For anything more, see the "General Developer Doucmentation" link on that software wiki, which points here.
The troubleshooting wiki page may also still be useful but likely outdated.