Add Note on where to configure DocSearch via Pull Request

Author: yasulab

app/views/plain_page/index.html.haml

@@ -13,6 +13,7 @@
         / Collect the nav links, forms, and other content for toggling
         #bs-example-navbar-collapse-1.collapse.navbar-collapse
           %ul.nav.navbar-nav.navbar-right
+            / DocSearch: https://github.com/algolia/docsearch-configs/blob/master/configs/coderdojo.json
             %li.search
               %input#searchbox{ :placeholder => "🔍 検索", :type => "text" }
               #hits