To run a NONMEM model, a NONMEM nmfeXX file is required, with XX the NONMEM version. When opening the NONMEM
command prompt, working directory is usually set to folder, where the nmfe file is located. When running NONMEM
from R (with the run_nm function), the path and the nmfe file must be provided (as the nm_path argument). To facilitate
the search for the nmfe file, this function can be used.