message: Add example to CMakeLists.txt
diff: @@ -24,6 +24,7 @@ list(APPEND ALL_EXE_SRCS
  ex15.cpp
  ex16.cpp
  ex17.cpp
  + ex18.cpp
  )
  if (MFEM_USE_MPI)
  @@ -45,6 +46,7 @@ if (MFEM_USE_MPI)
  ex15p.cpp
  ex16p.cpp
  ex17p.cpp
  + ex18p.cpp
  )
  endif()
  