minor typo cleanup

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-1382 remove note that cd is not implemented

Signed-off-by: Sam Kleinman <samk@10gen.com>
typo c/Mongo DB/MongoDB

Signed-off-by: Sam Kleinman <samk@10gen.com>
improving maxConns option reference
DOCS-1387 add unique option to shardCollection command

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-1354: minor tweak