Docs: fix some build warnings

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.

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]]