[HPC][Nways] explanation for the user of -DUSE_COUNTING_ITERATOR

[mozhgan-kch]

In the stdpar notebook, it is not clear as to why we are using the -DUSE_COUNTING_ITERATOR when compiling the code for the GPU. Having fixed paths to include libs and headers for NVTX at the compile-time confuses users as to why it is not needed when we compile for the GPU but it is needed for the multicore.