iPods: Allow using scroll wheel to change volume on QuickScreen

As suggested by forum user yuuiko

Change-Id: Ifb989f9513a9e3c59e4ab0f38c0a8e2675c68dd8

manual/main_menu/main.tex

@@ -250,6 +250,12 @@ utilities. A detailed description of the different plugins is to be found in
    Therefore if you select the same setting at e.g. the top and bottom of the
    quickscreen, then pressing up and down will cycle through this setting in
    opposite directions.
+
+  \opt{ipod}{
+    \note{You can always adjust the sound volume on the QuickScreen.
+    To do so, slide your finger around the click wheel as you would on the
+    While Playing Screen.}
+  }
 }
 
 \section{\label{ref:MainMenuShortcuts}Shortcuts}