Document second parameter (seek position) of /cat command

docs/help/in/cat.in

@@ -5,12 +5,16 @@
 
 %9Parameters:%9
 
-    The file to display.
+    The file to display and optionally a position to seek in the file,
+    in bytes.
 
 %9Description:%9
 
     Displays the contents of the specified file into the active window.
 
+    The seek position parameter is used internally to display away logs, if
+    omitted the whole file is shown.
+
 %9Examples:%9
 
     /CAT /etc/network/interfaces

src/fe-common/core/fe-core-commands.c

@@ -114,7 +114,7 @@ static void cmd_version(char *data)
 	}
 }
 
-/* SYNTAX: CAT <file> */
+/* SYNTAX: CAT <file> [<seek position>] */
 static void cmd_cat(const char *data)
 {
 	char *fname, *fposstr;