Add digest e-mails

db/migrate/20170303212857_add_last_emailed_at_to_users.rb

@@ -0,0 +1,5 @@
+class AddLastEmailedAtToUsers < ActiveRecord::Migration[5.0]
+  def change
+    add_column :users, :last_emailed_at, :datetime, null: true, default: nil
+  end
+end