cmap_track_add.3.in: fix typo: bellow -> below

Signed-off-by: Ferenc Wágner <wferi@niif.hu>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>

man/cmap_track_add.3.in

@@ -73,7 +73,7 @@ in callback)
 .PP
 .I notify_fn
 is pointer to function which is called when value is changed. It's definition and meaning of parameters
-is discussed bellow.
+is discussed below.
 .I user_data
 argument is passed directly to
 .I notify_fn