add dummy discovery controller

test/dummy/app/controllers/discovery_controller.rb

@@ -0,0 +1,7 @@
+class DiscoveryController < ApplicationController
+  def discovery
+    discovery = DiasporaFederation::Discovery::Discovery.new(params[:q])
+
+    render json: discovery.fetch
+  end
+end

test/dummy/config/routes.rb

@@ -1,3 +1,5 @@
 Rails.application.routes.draw do
   mount DiasporaFederation::Engine => "/"
+
+  get "discovery" => "discovery#discovery"
 end