runtime(doc): correct <PageUp>/<PageDown> behavior in 'wildmenu' (#13336)

"but don't insert it" is wrong.
Also move them just below <Up> <Down> as they are more similar.

Author: zeertzjq

runtime/doc/index.txt

@@ -1117,7 +1117,7 @@ commands in wildmenu mode (see 'wildmenu')
 		<Up>		move up to parent / select the previous match
 		<Down>		move down to submenu / select the next match
 		<Left>		select the previous match / move up to parent
-		<Down>		select the next match / move down to submenu
+		<Right>		select the next match / move down to submenu
 		<CR>		move into submenu when doing menu completion
 		other		stop completion and insert the typed character
 

runtime/doc/options.txt

@@ -9333,12 +9333,12 @@ A jump table for the options with a short description can be found at |Q_op|.
 	When using the popup menu for command line completion, the following
 	keys have special meanings:
 	<Up> <Down>	- select previous/next match (like CTRL-P/CTRL-N)
+	<PageUp>	- select a match several entries back
+	<PageDown>	- select a match several entries further
 	<Left>		- in filename/menu name completion: move up into
 			  parent directory or parent menu.
 	<Right>		- in filename/menu name completion: move into a
 			  subdirectory or submenu.
-	<PageUp>	- Select a match several entries back, but don't insert it.
-	<PageDown>	- Select a match several entries further, but don't insert it.
 	CTRL-E		- end completion, go back to what was there before
 			  selecting a match.
 	CTRL-Y		- accept the currently selected match and stop