Update help.html.erb

Fix for timwaters#242 !

app/views/home/help.html.erb

@@ -10,6 +10,7 @@ Common Problems:
   <li>The image from the URL doesn't work: Try downloading and uploading manually.</li>
   <li>How do I make a Mosaic from maps: Add the maps to your favourites first </li>
   <li>How do I make a delete a map?: Go to the Edit tab of your map and find the delete link </li>
+  <li>Where do I find a tutorial?: A web search will find the latest. But here's a <a href="https://programminghistorian.org/en/lessons/introduction-map-warper">great introduction</a>.
 </ul>
 
 <h4>Why can't I use google maps?</h4>