pro git link

index.html

@@ -16,7 +16,8 @@ layout: reference
     Each section will link to the next section, so it can be used
     as a tutorial.  Every page will also link to more in-depth
     Git documentation such as the offical manual pages and relevant
-    sections in the Pro Git book, so you can learn more about any of 
+    sections in the <a href="http://progit.org">Pro Git book</a>, 
+    so you can learn more about any of 
     the commands. First, we'll start with thinking about source code 
     management like Git does.
     </p>