Add wiki css to help page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/pages/help.scss

 .documentation-index {
-  h1 {
-    margin: 0;
-  }
-
-  h2 {
-    font-size: 20px;
-  }
-
   li {
     line-height: 24px;
     color: $document-index-color;

app/views/help/index.html.haml

@@ -29,7 +29,7 @@
 
 .row.prepend-top-default
   .col-md-8
-    .documentation-index
+    .documentation-index.wiki
       = markdown(@help_index)
   .col-md-4
     .panel.panel-default