Add a fix for the error svg illegal namespace

Guides/wiki.md

@@ -116,6 +116,9 @@ cd /var/www/mediawiki/extensions/
 
 sudo git clone https://github.com/mgeb/mediawiki-drawio-editor DrawioEditor
 ```
+
+**Fix SVG upload** : add `http://www.w3.org/1999/xhtml` in `/var/www/mediawiki/includes/upload/UploadBase.php`.
+
 ## Uninstall Mediawiki
 
 ### Disable site