docs: Added a tutorial by Giuseppe Cassibba.

Also fixed up trailing whitespace.

docs.html

@@ -75,6 +75,9 @@
 	<a href="http://www.penguin-breeder.org/sane/saned/" target="_top">Saned, the SANE Network
 	Scanning Daemon</a>: How to set up the SANE Network Daemon is explained here.
       </li>
+      <li>
+	<a href="https://peppe8o.com/scan-from-raspberry-pi-terminal-with-sane/" target="_top"> SANE and a Raspberry PI</a>: How to use SANE with Raspberry PI terminal, plus Project to upgrade a scanner to Scan-to-Mail, by Giuseppe Cassibba.
+      </li>
     </ul>
 
     <h2>Programmer's Documentation</h2>