xset: add enable/disable DPMS examples (#7617)

pages/linux/xset.md

@@ -10,3 +10,11 @@
 - Set the screensaver to start after 60 minutes of inactivity:
 
 `xset s 3600 3600`
+
+- Disable DPMS (Energy Star) features:
+
+`xset -dpms`
+
+- Enable DPMS (Energy Star) features:
+
+`xset +dpms`