blktrace: Document default values for -b and -n

To help users better deal with the log message
 "You have dropped events, consider using a larger buffer size (-b)",
it's helpful to list the defaults for sub buffer management, without
flags.

Signed-off-by: Justin TerAvest <teravest@google.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
1 file changed