Merge #1806

1806: Reflect override settings for postfix r=mergify[bot] a=ineiti

## What type of PR?

(documentation)

## What does this PR do?

Fixes path in the documentation setting, and also adds how to change postfix.cf

Co-authored-by: Linus Gasser <linus.gasser@epfl.ch>

docs/faq.rst

@@ -261,6 +261,8 @@ correct syntax. The following file names will be taken as override configuration
    - ``main.cf`` as ``$ROOT/overrides/postfix/postfix.cf``
    - ``master.cf`` as ``$ROOT/overrides/postfix/postfix.master``
    - All ``$ROOT/overrides/postfix/*.map`` files
+   - For both ``postfix.cf`` and ``postfix.master``, you need to put one configuration per line, as they are fed line-by-line
+     to postfix.
 - `Dovecot`_ - ``dovecot.conf`` in dovecot sub-directory;
 - `Nginx`_ - All ``*.conf`` files in the ``nginx`` sub-directory;
 - `Rspamd`_ - All files in the ``rspamd`` sub-directory.