Document varnishstat ncurses up/down bindings

And avoid magic ASCII numbers when we could use character literals
instead.

bin/varnishstat/varnishstat_curses.c

@@ -871,13 +871,13 @@ handle_keypress(int ch)
 {
 	switch (ch) {
 	case KEY_UP:
-	case 107:  /* k */
+	case 'k':
 		if (current == 0)
 			return;
 		current--;
 		break;
 	case KEY_DOWN:
-	case 106:  /* j */
+	case 'j':
 		if (current == n_ptarray - 1)
 			return;
 		current++;

doc/sphinx/reference/varnishstat.rst

@@ -73,10 +73,10 @@ Key bindings
 
 The following keys control the interactive display:
 
-<UP>
+<UP> or <k>
 	Navigate the counter list one line up.
 
-<DOWN>
+<DOWN> or <j>
 	Navigate the counter list one line down.
 
 <PAGEUP> or <b> or <CTRL-b>