text can just be the path to NMTRAN.exe in which case
nm_tran_command will use the format /path/to/NMTRAN.exe < {ctl_name} to
launch NMTRAN.exe where {ctl_name} is the name of the control file.
Specifying
nm_tran_command("/path/to/NMTRAN.exe < {ctl_name}") is equivalent to:
nm_tran_command("/path/to/NMTRAN.exe")
More complicated formats are possible with different installations which
can be seen examples.
As with all NMproject configuration options set this up either at the
beginning of your script, in your .Rprofile or for all users in
Rprofile.site. See FAQ for setting up configuration options permanently.