Add readme for example

README.md

@@ -11,3 +11,16 @@ Copy migrations to your project
     $ rails g acts_as_pasting:migrations
 
 TODO: Write usage instructions here
+
+```ruby
+class Teacher < ApplicationRecord
+  include ActsAsPasting::Pasted
+  pasted_with ::Duty
+  acts_as_pasted :duties, source_type: 'Duty'
+end
+
+class Duty < ApplicationRecord
+  include ActsAsPasting::Pastable
+  acts_as_pastable :teachers, source_type: 'Teacher'
+end
+```