/dmails: add help:dmail link to subnavbar.

app/views/dmails/_secondary_links.html.erb

@@ -4,8 +4,11 @@
     <li><%= link_to "All", all_dmails_path(set_default_folder: true) %></li>
     <li><%= link_to "Received", received_dmails_path(set_default_folder: true) %></li>
     <li><%= link_to "Sent", sent_dmails_path(set_default_folder: true) %></li>
+    <li>|</li>
     <li><%= link_to "New", new_dmail_path %></li>
     <li><%= link_to "Search", search_dmails_path %></li>
     <li><%= link_to "Mark all as read", {:controller => "dmails", :action => "mark_all_as_read"}, :method => :post, :remote => true %></li>
+    <li>|</li>
+    <li><%= link_to "Help", wiki_pages_path(title: "help:dmail") %></li>
   </menu>
 <% end %>