README.md in upsert-1.1.7 vs README.md in upsert-1.2.0

@@ -23,11 +23,13 @@
 ```ruby
 connection = Mysql2::Client.new([...])
 table_name = :pets
 upsert = Upsert.new connection, table_name
 # N times...
-upsert.row({:name => 'Jerry'}, :breed => 'beagle')
+upsert.row({:name => 'Jerry'}, :breed => 'beagle', :created_at => Time.now)
 ```
+
+The `created_at` and `created_on` columns are used for inserts, but ignored on updates.
 
 So just to reiterate you've got a __selector__ and a __setter__:
 
 ```ruby
 selector = { :name => 'Jerry' }