[archives] better description of the old archive on the contact page.

html/contact.html

@@ -148,7 +148,14 @@ function(err, data) {
                 <div class="side-item">
                   <div class="icon-com"><img src="/assets/img/community/mails.png"/></div>
                   <a href="/html/fc-discuss/archives.html">
-                    Archives of the Old Frama-C discuss list (before October 2020)
+                    <div class="caption">
+                    Archives of the old Frama-C discuss list
+                    </div>
+                    <div class="description">
+                      Archives up to October 2020 (when the list was managed through
+                      another provider). Newer archives can be found at the site of
+                      the current mailing list.
+                    </div>
                   </a>
 		</div>
 		<div class="side-item">