Add a link to the media wiki backup page

Guides/wiki.md

@@ -132,3 +132,9 @@ DROP ROLE wiki_app ;
 ```
 sudo rm -r /var/www/mediawiki
 ```
+
+## Backup Wiki
+
+[https://www.mediawiki.org/wiki/Manual:Backing_up_a_wiki](Backing up a wiki)
+
+See the `ServerScripts/Backup` folder.