README.md in spot-rate-0.2.0 vs README.md in spot-rate-0.4.0

@@ -32,9 +32,11 @@
 
 If you'd like to register your own currency converter, use the
 `.register_currency_converter` method:
 
 ```ruby
+require 'spot-rate'
+
 class MyRandomCurrencyConverter
   def initialize from_currency, to_currency
     @from_currency = from_currency
     @to_currency   = to_currency
   end