Adding sound effects to Clone tool

Source https://commons.wikimedia.org/wiki/File:Sheep_bleating.ogg
(Public domain)

docs/AUTHORS.txt

@@ -2,12 +2,12 @@ AUTHORS.txt for Tux Paint
 
 Tux Paint - A simple drawing program for children.
 
-Copyright (c) 2002-2020
+Copyright (c) 2002-2021
 Various contributors (see below, and CHANGES.txt)
 http://www.tuxpaint.org/
 
 
-June 17, 2002 - August 29, 2020
+June 17, 2002 - February 10, 2021
 
 $Id$
 
@@ -358,6 +358,10 @@ $Id$
   * Cartoon
     * "cartoon6.wav" from http://www.grsites.com/
 
+  * Clone
+    * https://commons.wikimedia.org/wiki/File:Sheep_bleating.ogg
+      Public domain
+
   * Many others taken from various sources on the web.
 
   * Edited using SOX