new action for intro page for new users

app/presenters/intro_presenter.rb

@@ -0,0 +1,11 @@
+class IntroPresenter
+  def popular_tags
+    Tag.order("post_count desc").limit(8).map(&:name)
+  end
+
+  def each
+    popular_tags.each do |tag|
+      yield(tag, PostSets::Post.new(tag, 1, 6))
+    end
+  end
+end