Format README

Author: Kimmie

README.md

@@ -38,9 +38,13 @@ class Member
  attr_accessor :social_insurance_number
  validates :social_insurance_number, luhn_algorithm: true
 end
+```
+
 ```
 person = Member.new(social_insurance_number: 'a valid number')
+
 person.valid? # => true
+```
 
 You can also pass in a customized message when validating an attribute with Luhn Algorithm, for example