Merge branch 'custom-404' into 'develop'

custom instructions for 404 page

See merge request R3/howto-cards!44

404.html

@@ -21,4 +21,9 @@ layout: default
 
   <p><strong>Page not found :(</strong></p>
   <p>The requested page could not be found.</p>
+  <p>All cards are available from here: <a href="https://howto.lcsb.uni.lu">https://howto.lcsb.uni.lu</a></p>
+  <p><i>Please note: Some cards are only available from within the university network. Please
+          reload the page when connected using <a href="https://vpn.uni.lu"><strong>VPN</strong></a>
+         (from outside the university network)
+         or when connected to the <strong>eduroam</strong> network.</i></p>
 </div>