Escape literal \n

Otherwise it isn't rendered correctly.

doc/man1/rigctld.1

@@ -211,7 +211,7 @@ Use
 .I char
 as separator instead of line feed.
 .IP
-The default is \n.  Recommend using $ or @ as they work on both Unix and Windows
+The default is \(oq\\n\(cq.  Recommend using $ or @ as they work on both Unix and Windows.
 .IP
 .
 .TP