Update docs to point to new tutorial

Replaced the link at the top of the manual.  Remove reference to
old tutorial doc.  Added an obsolescence notice to the top of the
old tutorial.  Updated tutorial message and link in README.

Also, fixed sidenav style.

docs/main.css

@@ -156,10 +156,10 @@ kbd.key {
     margin: 0;
 }
 #sidenav li {
-    padding: 0 0px 1px 0;      /* top right bottom left */
+    padding: 0 0 1px 0;      /* top right bottom left */
 }
 #sidenav ul ul li {
-    padding: 0 0 1px 10px;      /* top right bottom left */
+    padding: 1px 0 0 10px;      /* top right bottom left */
 }
 #sidenav a {
     color: #ffffff;