message: helloBPReader - add selection so mpirun -n 2 works.
  If the writer is run with mpirun -n 3, the reader needs
  to handle it with a selection.
diff: * helloBPReader.cpp: Simple self-descriptive example of how to read a variable
  * to a BP File.
  *
  + * Try running like this from the build directory:
  + * mpirun -np 3 ./bin/hello_bpReader
  + *
  * Created on: Feb 16, 2017
  * Author: William F Godoy godoywf@ornl.gov
  */
  @@ -63,6 +66,8 @@ int main(int argc, char *argv[])
  if (bpFloats) // means found
  {
  + // read only the chunk corresponding to our rank
  + bpFloats.SetSelection({{Nx * rank}, {Nx}});
  // myFloats.data is pre-allocated
  bpReader.Get<float>(bpFloats, myFloats.data(), adios2::Mode::Sync);
  @@ -76,6 +81,8 @@ int main(int argc, char *argv[])
  if (bpInts) // means not found
  {
  + // read only the chunk corresponding to our rank
  + bpInts.SetSelection({{Nx * rank}, {Nx}});
  // myInts.data is pre-allocated
  bpReader.Get<int>(bpInts, myInts.data(), adios2::Mode::Sync);
  