message: Adding a short comment block to an example
diff: // MFEM Brick Eigenvalue test
  //
  +// To test the ND_TetrahedronElement this should be run with the "-m
  +// 13" command line option to request a tetrahedral mesh. To test
  +// face dof orientations the basis function order should be set to at
  +// least 3 for tetrahedral elements (2 for hexahedral elements).
  +//
  +// The eigenvalues for the 2D meshes should come out to be 1, 2, and 3.
  +// The eigenvalues for the 3D meshes should come out to be 3, 4, and 5.
  #include "mfem.hpp"
  #include <fstream>
  