fix 404 and formatting on homepage

Author: adamjonas

index.html

@@ -40,8 +40,8 @@
 
   <div class="dah_card">
     <p><b>Review a PR</b></p>
-    <p>Prevent problems before they affect your bitcoins  Choose a PR to
-    review and <a href="404">learn as you go</a>.</p>
+    <p>Prevent problems before they affect your bitcoins. Choose a PR to
+    review and learn as you go.</p>
   </div>
 
   <div class="dah_card">