Add index to local census records document_number

This will speed up searching by document_number

db/migrate/20190509085124_add_index_to_local_census_records_document_number.rb

@@ -0,0 +1,5 @@
+class AddIndexToLocalCensusRecordsDocumentNumber < ActiveRecord::Migration[5.0]
+  def change
+    add_index :local_census_records, :document_number
+  end
+end

db/schema.rb

@@ -978,6 +978,7 @@ ActiveRecord::Schema.define(version: 20190607160900) do
     t.string   "postal_code",     null: false
     t.datetime "created_at",      null: false
     t.datetime "updated_at",      null: false
+    t.index ["document_number"], name: "index_local_census_records_on_document_number", using: :btree
   end
 
   create_table "locks", force: :cascade do |t|