Include the helper for mailer, add links to emails.

app/mailers/notify.rb

@@ -11,6 +11,7 @@ class Notify < ActionMailer::Base
   add_template_helper ApplicationHelper
   add_template_helper GitlabMarkdownHelper
   add_template_helper MergeRequestsHelper
+  add_template_helper EmailsHelper
 
   default_url_options[:host]     = Gitlab.config.gitlab.host
   default_url_options[:protocol] = Gitlab.config.gitlab.protocol

app/views/layouts/notify.html.haml

@@ -28,3 +28,4 @@
           You're receiving this notification because you are a member of the #{link_to_unless @target_url, @project.name_with_namespace, project_url(@project)} project team.
         - if @target_url
           #{link_to "View it on GitLab", @target_url}
+          = email_action name: "View #{@note.noteable_type.underscore.humanize}", url: @target_url