minor: clarifying mongodump oplog option.

Author: Sam Kleinman

source/reference/mongodump.txt

@@ -145,11 +145,16 @@ Options
 
 .. option:: --oplog
 
-   Use this option to ensure that the database backup you create is a
-   consistent point-in-time snapshot of the state of a
-   database. Without this option, changes made to the database during
-   the update process may cause the backup to reflect an inconsistent
-   status.
+   Use this option to ensure that :program:`mongodump` creates a dump
+   of the database that includes an :term:`oplog`, to create a
+   point-in-time snapshot of the state of a MongoDB instance. To
+   restore to a specific point-in-time backup, use the output created
+   with this option n conjunction with :option:`mongorestore --oplogReplay`.
+
+   Without :option:`--oplog`, if there are write operations during the
+   dump operation, the dump will not reflect a single moment in
+   time. Changes made to the database during the update process can
+   affect the output of the backup.
 
    :option:`--oplog` has no effect when running :program:`mongodump`
    against a :program:`mongos` instance to dump the entire contents of

source/reference/mongorestore.txt

@@ -139,7 +139,7 @@ Options
 
 .. option:: --oplogReplay
 
-   Replays the oplog after the data is restored to ensure that the current  
+   Replays the oplog after restoring the dump to ensure that the current
    state of the database reflects the point-in-time backup captured with
    the ":option:`mongodump --oplog`" command.