Added update note on tutorials page.

examples/hakyll/templates/tutorials.html

@@ -5,3 +5,10 @@
 <ul>
     $body
 </ul>
+<p>
+    All these tutorials assume you are using the latest stable version of
+    Hakyll. If this is not the case, you might want to update using:
+    <pre><code>ghc-pkg unregister hakyll
+cabal update
+cabal install hakyll</code></pre>
+</p>