Add another reference for pretalx format

app/jobs/pretalx/import_job.rb

@@ -3,6 +3,7 @@ require 'httparty'
 module Pretalx
   # See https://c3voc.de/wiki/schedule for more information about the format
   # Schema: https://c3voc.de/schedule/schema.json
+  # For the different sources from Hub, see https://c3voc.de/wiki/events:38c3:schedule
   class ImportJob < ApplicationJob
     queue_as :default
     include ActionView::Helpers