def render_opml(list)
      document = Nokogiri::XML(list.load_list)
      feeds.each do |feed_url|
        node = "<outline xmlUrl='#{feed_url}' />\n"
        document.xpath("//outline[@text='Subscriptions']").last.add_child node
      end
      formatted_no_decl = Nokogiri::XML::Node::SaveOptions::FORMAT +
                          Nokogiri::XML::Node::SaveOptions::NO_DECLARATION
      document.to_xml(encoding: 'utf-8', save_with: formatted_no_decl)
    end
def render_opml(list)
      document = Nokogiri::XML(list.load_list)
      feeds.each do |feed_url|
        node = "<outline xmlUrl='#{feed_url}' />\n"
        document.xpath("//outline[@text='Subscriptions']").last.add_child node
      end
      formatted_no_decl = Nokogiri::XML::Node::SaveOptions::FORMAT +
                          Nokogiri::XML::Node::SaveOptions::NO_DECLARATION
      document.to_xml(encoding: 'utf-8', save_with: formatted_no_decl)
    end
Append feeds to current subscription list and return XML document

 @return [String]