Find the code and more instructions on GitHub.
If you want to jump right in, run the following to immediately start integrating the scalar three-loop mercedes diagram,
git clone https://github.com/alphal00p/gammaloop.git && cd gammaloop
./bin/compile.sh
./bin/gammaloop example/cards/scalar_mercedes.gL
or a one-loop hexagon diagram from the scattering process (through a top-quark loop) with:
./bin/gammaloop examples/cards/physical_1L_AA_AAAA.gL
Additional information can be found on this wiki, especially regarding syntax for process generation.