Surprisingly building and running a Fortran program on Linux is super easy.
Assuming you are on any flavor of Linux, from the command line clone the repository, cd into it and run:
make
That's it!
./rpg
Open and edit any of the .f90 files to see the code. Even without knowing Fortran, it isn't hard to comprehend what is happening and tweak the existing code.
Make some changes, make a pull request, and be a Fortran coder on GitHub!