Update overrides faq for include roundcube

docs/faq.rst

@@ -267,6 +267,7 @@ correct syntax. The following file names will be taken as override configuration
 - `Dovecot`_ - ``dovecot.conf`` in dovecot sub-directory;
 - `Nginx`_ - All ``*.conf`` files in the ``nginx`` sub-directory;
 - `Rspamd`_ - All files in the ``rspamd`` sub-directory.
+- Roundcube - All ``*.inc`` files in the ``roundcube`` sub directory.
 
 To override the root location (``/``) in Nginx ``WEBROOT_REDIRECT`` needs to be set to ``none`` in the env file (see :ref:`web settings <web_settings>`).