Merge #1141

1141: Docs: fix some build warnings r=mergify[bot] a=muhlemmer

## What type of PR?
Documentation

## What does this PR do?

I've noticed some styling / flow errors on the FAQ page on mailu.io.
This was due to short underlining.
Spynx was complaining about this at build time.

## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [x] In case of feature or enhancement: documentation updated accordingly
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.


Co-authored-by: Tim Möhlmann <muhlemmer@gmail.com>

docs/cli.rst

@@ -29,7 +29,7 @@ alias-delete
 
 
 domain
-----
+------
 
 .. code-block:: bash
 

docs/faq.rst

@@ -243,7 +243,7 @@ correct syntax. The following file names will be taken as override configuration
 *Issue reference:* `206`_.
 
 I want to integrate Nextcloud 15 (and newer) with Mailu
-````````````````````````````````````````
+```````````````````````````````````````````````````````
 
 1. Enable External user support from Nextcloud Apps interface
 
@@ -270,7 +270,7 @@ After successfull login the domain part will be striped and the rest used as use
 *Issue reference:* `575`_.
 
 I want to integrate Nextcloud 14 (and older) with Mailu
-````````````````````````````````````````
+```````````````````````````````````````````````````````
 
 1. Install dependencies required to authenticate users via imap in Nextcloud
 
@@ -340,8 +340,8 @@ down and up again. A container restart is not sufficient.
 
 *Issue reference:* `615`_.
 
-Access Denied Errors
---------------------
+403 - Access Denied Errors
+---------------------------
 
 While this may be due to several issues, check to make sure your ``DOMAIN=`` entry is the **first** entry in your ``HOSTNAMES=``.
 

docs/reverse.rst

@@ -154,7 +154,7 @@ If your Traefik is configured to automatically request certificates from *letsen
 and this is the ``DOMAIN`` in your ``.env``?
 To support that use-case, Traefik can request ``SANs`` for your domain. Lets add something like
 
-.. code-block:: guess
+.. code-block:: yaml
 
   [acme]
     [[acme.domains]]