Tweak M80/M81 descriptions

Marlin/Marlin_main.cpp

@@ -97,8 +97,8 @@
  * M76  - Pause the print job timer.
  * M77  - Stop the print job timer.
  * M78  - Show statistical information about the print jobs. (Requires PRINTCOUNTER)
- * M80  - Turn on Power Supply. (Requires POWER_SUPPLY)
- * M81  - Turn off Power Supply. (Requires POWER_SUPPLY)
+ * M80  - Turn on Power Supply. (Requires POWER_SUPPLY > 0)
+ * M81  - Turn off Power Supply. (Requires POWER_SUPPLY > 0)
  * M82  - Set E codes absolute (default).
  * M83  - Set E codes relative while in Absolute (G90) mode.
  * M84  - Disable steppers until next move, or use S<seconds> to specify an idle