Minor tweak to the vadvise entry.

UPDATING

@@ -1,4 +1,4 @@
-$NetBSD: UPDATING,v 1.289 2017/12/26 20:04:03 christos Exp $
+$NetBSD: UPDATING,v 1.290 2017/12/27 08:29:02 martin Exp $
 
 This file (UPDATING) is intended to be a brief reference to recent
 changes that might cause problems in the build process, and a guide for
@@ -26,7 +26,7 @@ Recent changes:
 		cd $OBJ && find . -type d -name libc | xargs rm -rf
 	For architectures that support multiple "compat" binary targets,
 	you'll need to cleanup both the regular libc directory and the
-	compat one.
+	compat ones (the above command will do that).
 
 20171010:
 	a change to the build structure of external/bsd/acpica/bin/iasl