LU-10965 doc: add mirror options to "lfs find" in lfs.1

LU-10965 doc: add mirror options to "lfs find" in lfs.1

This patch adds the following mirror related search
options to "lfs find" command in lfs man page:

[[!] --mirror-count|-N [+-]n]
[[!] --mirror-state <[^]state>]

The usage of the options are explained in separate
"lfs find" man page.

Change-Id: I13c19be01cb050cd5035d9058bbd6fc7d2f50564
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: https://review.whamcloud.com/32201
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>