[Rspamd] domain-wide-footer update description

data/web/lang/lang.de-de.json

@@ -583,7 +583,7 @@
         "domain_admin": "Domain-Administrator bearbeiten",
         "domain_footer": "Domain wide footer",
         "domain_footer_html": "HTML footer",
-        "domain_footer_info": "Domain wide footer werden allen E-Mails hinzugefügt, die von der angegebenen Domain gesendet werden.",
+        "domain_footer_info": "Domain wide footer werden allen ausgehenden E-Mails hinzugefügt, die einer Adresse innerhalb dieser Domain gehört.<br>Die folgenden Variablen können für den Footer benutzt werden:",
         "domain_footer_plain": "PLAIN footer",
         "domain_quota": "Domain Speicherplatz gesamt (MiB)",
         "domains": "Domains",

data/web/lang/lang.en-gb.json

@@ -585,7 +585,7 @@
         "domain_admin": "Edit domain administrator",
         "domain_footer": "Domain wide footer",
         "domain_footer_html": "HTML footer",
-        "domain_footer_info": "Domain wide footers will be added to all emails sent from the specified domain.",
+        "domain_footer_info": "Domain-wide footers are added to all outgoing emails associated with an address within this domain. <br> The following variables can be used for the footer:",
         "domain_footer_plain": "PLAIN footer",
         "domain_quota": "Domain quota",
         "domains": "Domains",

data/web/templates/edit/domain.twig

@@ -281,7 +281,12 @@
                   <div class="col-sm-12">
                     <h4>{{ lang.edit.domain_footer }}</h4>
                     <p>{{ lang.edit.domain_footer_info|raw }}</p>
-                    <form class="form-horizontal" data-id="domain_footer">
+                    <pre>{= auth_user =}   - Authenticated Username specified by an MTA
+{= from_user =}   - Parsed user part of email headers, e.g for "moo@mailcow.tld" it returns "moo"
+{= from_name =}   - Parsed name of email headers, e.g for "Mailcow &lt;moo@mailcow.tld&gt;" it returns "Mailcow"
+{= from_addr =}   - Parsed address part of email headers
+{= from_domain =} - Parsed domain part of email headers</pre>
+                    <form class="form-horizontal mt-4" data-id="domain_footer">
                       <div class="row mb-2">
                         <label class="control-label col-sm-2" for="domain_footer_html">{{ lang.edit.domain_footer_html }}:</label>
                         <div class="col-sm-10">