Tip for fixing annoying firewall connections

Student connections may be more restrictive and require a TURN server.

Guides/nextcloud.md

@@ -61,3 +61,9 @@ To enable *mod_headers* on HTTPD : `a2enmod headers`
 ## Other fixes
 
 As an admin, go to _Overview_ in the _Administration_ panel from _Settings_. Nexctloud will scan your instance and give you instructions.
+
+## TURN Talk
+
+Talk can fail for some users behind annoying firewalls or symmetric NAT.
+
+That can be fixed by using a [TURN server](https://nextcloud-talk.readthedocs.io/en/latest/TURN/).