updated the docs

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403026

docs/docs/api.xml

@@ -1033,6 +1033,9 @@
                   <a href="dlib/threads/auto_mutex_extension.h.html">here</a>.
                </description> 
 
+               <examples>
+                  <example>threads_ex.cpp.html</example>
+               </examples>
                
             </extension>
             <extension>