doc: update pools documentation

set=>get in "Get Pool Values"
grep for 'replicated size', not 'rep size'

Signed-off-by: Kevin Dalley <kevin@kelphead.org>
Merge pull request #1886 from nereocystis/pools-doc

doc: update pools documentation

Reviewed-by: Loic Dachary <loic@dachary.org>