Update preferences' description for debug display

Author: moondroidcoder

source/funkin/Preferences.hx

@@ -137,6 +137,7 @@ class Preferences
 
   /**
    * If enabled, an FPS and memory counter will be displayed even if this is not a debug build.
+   * Always disabled on release mobile builds.
    * @default `Off`
    */
   public static var debugDisplay(get, set):DebugDisplayMode;