doc: Fix macchanger.

wiki/src/doc/advanced_topics/mac_changer.mdwn

 [[!meta title="Enable MAC Changer"]]
 
-**FIXME**: This section have not been adapted now. Macchanger is not easily
-usable in Tails now (0.7.2)
+<div class="bug">
+<p>Macchanger is shipped in Tails but there is currently no documented method of
+using it.</p>
 
-If you paid attention when you started up Tails you may have noticed
-an odd option in the language selection menu, namely the "Enable MAC
-changer" entry. Some further explanation is probably required in order
-to understand whether this is relevant for you or not.
+<p>[[See the corresponding ticket.|todo/macchanger/]]</p>
+</div>
 
 First of all, you should know that all network cards, both wired and
 wireless, have a unique identifier stored in them called their MAC