Sorry, the instructions were a bit terse indeed. To use the scripts you need to build and install the CTL interpreter from GitHub - ampas/CTL: The Color Transformation Language (CTL). I don’t think there are pre-built packages for this (but I might be wrong). Once installed, you need to tell ART where to find the CTL headers and libraries. Assuming you installed in /usr/local (the default), this should do:
cmake -DENABLE_CTL=1 -DCTL_INCLUDE_DIR=/usr/local/include/CTL /path/to/ART
HTH