LUDOC-108 dne: Manual includes DNE usage instructions.

LUDOC-108 dne: Manual includes DNE usage instructions.

The manual now includes instructions to:
- add a MDT.
- remove a MDT.
- upgrade to multiple MDT configurations.
- designing active-active MDS configurations.
- warns against having chained remote directories.
- added administrative documentation for lfs.

Signed-off-by: Richard Henwood <richard.henwood@intel.com>
Change-Id: I9b4fb35d7932b9e90561e03b0b72271b9c2728cf
Reviewed-on: http://review.whamcloud.com/4773
Tested-by: Hudson