fix typo on the main page

Author: Hristo Hristov

index.html

@@ -28,7 +28,7 @@ <h2>Introduction to the Git Reference</h2>
   <h2>How to Think Like Git</h2>
   <div class="block">
     <p>
-    This first thing that is important to understand about Git is
+    The first thing that is important to understand about Git is
     that it thinks about version control very differently than 
     Subversion or Perforce or whatever SCM you may be used to. It
     is often easier to learn Git by trying to forget your assumptions