Switch to the book intro

... rather than the 30 minute intro.

Author: steveklabnik

index.html

@@ -11,7 +11,7 @@
           prevents almost all crashes<span class="asterisk">*</span>,
           and eliminates data races.
           <br/>
-          <a href="http://doc.rust-lang.org/nightly/intro.html">Show me more!</a>
+          <a href="http://doc.rust-lang.org/nightly/book/README.html">Show me more!</a>
         </p>
       </div>
       <div class="col-md-4 install-box">