docs: refer to the FAQ when <Alt+Up> does nothing on a Linux console

doc/nano.texi

@@ -1471,10 +1471,14 @@ Goes one line down (in the editor or browser).
 @item scrollup
 Scrolls the viewport up one row (meaning that the text slides down)
 while keeping the cursor in the same text position, if possible.
+(This function is bound by default to <Alt+Up>.
+If <Alt+Up> does nothing on your Linux console, see the FAQ:
+@url{https://nano-editor.org/dist/latest/faq.html#4.1}.)
 
 @item scrolldown
 Scrolls the viewport down one row (meaning that the text slides up)
 while keeping the cursor in the same text position, if possible.
+(This function is bound by default to <Alt+Down>.)
 
 @item center
 Scrolls the line with the cursor to the middle of the screen.

doc/nanorc.5

@@ -713,10 +713,15 @@ Goes one line down (in the editor or browser).
 .B scrollup
 Scrolls the viewport up one row (meaning that the text slides down)
 while keeping the cursor in the same text position, if possible.
+(This function is bound by default to <Alt+Up>.
+If <Alt+Up> does nothing on your Linux console, see the FAQ:
+.UR https://nano\-editor.org/dist/latest/faq.html#4.1
+.UE .)
 .TP
 .B scrolldown
 Scrolls the viewport down one row (meaning that the text slides up)
 while keeping the cursor in the same text position, if possible.
+(This function is bound by default to <Alt+Down>.)
 .TP
 .B center
 Scrolls the line with the cursor to the middle of the screen.