fixing typo

Signed-off-by: Sam Kleinman <samk@10gen.com>
Update resync-replica-set-member.txt

Signed-off-by: Sam Kleinman <samk@10gen.com>
Update replica-set-sync.txt

There were some missing articles and other little words here and there. Tried to fill in what was missing to improve clarity.

Signed-off-by: Sam Kleinman <samk@10gen.com>