Show update when editing an article

app/views/articles/_form.html.haml

@@ -3,16 +3,16 @@
 
   .field
     = f.label :title
-    = f.text_field :title, :tabindex => 1, :autofocus => true
+    = f.text_field :title, :autofocus => true
     %span.hint Create a short and descriptive title for your post.
   .field
     = f.label :url
-    = f.text_field :url, :tabindex => 2
+    = f.text_field :url
     %span.hint The url you want to link to.
   .field
     = f.label :body
-    = f.text_area :body, "data-preview" => true, :tabindex => 3
+    = f.text_area :body, "data-preview" => true
   .control-bar
-    = f.submit 'Post!', :tabindex => 5
+    = f.submit @article.new_record? ? 'Post' : 'Update'
     or
     = link_to "get me out of here", root_path