Add create_on_open option

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

 Please enter the commit message for your changes. Lines starting
diff --git a/HOWTO b/HOWTO
index b8a7dd7..2cfe369 100644
--- a/HOWTO
+++ b/HOWTO
@@ -693,6 +693,9 @@
 create_fsync=bool	fsync the data file after creation. This is the
 			default.
 
+create_on_open=bool	Don't pre-setup the files for IO, just create open()
+			when it's time to do IO to that file.
+
 unlink=bool	Unlink the job files when done. Not the default, as repeated
 		runs of that job would then waste time recreating the file
 		set again and again.