Updated Usage (markdown)

Usage.md

@@ -59,7 +59,7 @@ optional args:
  -r      use advcpmv patched cp, mv
  -R      no rollover at edges
  -s name load session by name
- -S      du mode
+ -S      persistent session
  -t secs timeout to lock
  -T key  sort order [a/d/e/r/s/t/v]
  -V      show version