Add pread/pwrite support to sync engine

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 5d757b2..24171e9 100644
--- a/HOWTO
+++ b/HOWTO
@@ -314,6 +314,8 @@
 			sync	Basic read(2) or write(2) io. lseek(2) is
 				used to position the io location.
 
+			psync 	Basic pread(2) or pwrite(2) io.
+
 			libaio	Linux native asynchronous io.
 
 			posixaio glibc posix asynchronous io.