Minor documentation improvements
Minor documentation improvements

* Remove redundant hint to create namespace, role, and role bindings
  (already noted before)
* Refer to node settings under cluster `nodes` setting

Signed-off-by: Timoses <dcdc76fbca7007e663ee7730a97eee5cf83f5fae@gmail.com>

rook/rook,rook/nfs,rook/rook,rook/rook,rook/nfs,rook/nfs,rook/rook,rook/rook