PLUMED can be incorporated into gromacs using the standard patching procedure. Patching must be done in the gromacs source directory after gromacs has been configured but before gromacs is compiled. Gromacs should be configured with ./configure (not cmake).
To enable PLUMED in a gromacs simulation one should use mdrun with an extra -plumed flag. The flag can be used to specify the name of the PLUMED input file, e.g.:
mdrun -plumed plumed.dat
For more information on gromacs you should visit http://www.gromacs.org