Add cache parameter to fix the LocalConfig.php

Needed because of account errors.

Guides/wiki.md

@@ -85,6 +85,18 @@ Make the folder `/var/www/mediawiki` served by _httpd_.
 
 Then open the url : `http://domain.com/mw-config`
 
+At the end, you have to download the `LocalConfig.php` file.
+
+Put it in the folder `/var/www/mediawiki`.
+
+BEWARE : if you have enabled the accelerated cache, you have to add this line to the `LocalConfig.php` file :
+
+```
+$wgSessionCacheType = CACHE_DB;
+```
+
+Note : if you don't, the wiki can work but it would be impossible to log in or to create any account.
+
 ### Apache HTTPS
 
 _todo_