message: Added the 3D sample run.
diff: // mpirun -np 4 pmesh-optimizer -o 3 -rs 0 -mid 1 -tid 1 -ni 100 -ls 2 -li 100 -bnd -qt 1 -qo 8 -lim -lc 0.15
  // ICF combo shape + size (rings):
  // mpirun -np 4 pmesh-optimizer -o 3 -rs 0 -mid 1 -tid 1 -ni 100 -ls 2 -li 100 -bnd -qt 1 -qo 8 -cmb
  +// 3D pinched sphere shape (the mesh is in the mfem/data Github repository):
  +// mpirun -np 4 pmesh-optimizer -m ../../../mfem_data/ball-pert.mesh -o 4 -rs 0 -mid 303 -tid 1 -ni 20 -ls 2 -li 500 -fix-bnd
  +
  #include "mfem.hpp"
  using namespace mfem;
  