LU-8311 doc: add NIDs examples to mkfs.lustre and mount.lustre

LU-8311 doc: add NIDs examples to mkfs.lustre and mount.lustre

This patch adds examples of how NIDs can be specified on
mkfs.lustre and mount command lines.

Test-Parameters: trivial

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I93a8f843755582f94844504f604409dd43b617f9
Reviewed-on: http://review.whamcloud.com/23355
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Zhiqi Tao <zhiqi.tao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>