Add support for specifying UID/GID

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 0b40f75..45a96bb 100644
--- a/HOWTO
+++ b/HOWTO
@@ -1015,6 +1015,11 @@
 		the documentation that comes with the kernel, allowed values
 		are in the range of 100..1000.
 
+uid=int		Instead of running as the invoking user, set the user ID to
+		this value before the thread/process does any work.
+
+gid=int		Set group ID, see uid.
+
 6.0 Interpreting the output
 ---------------------------