more info about migration on readme

README.md

@@ -46,15 +46,19 @@ rake gems:install
 
 #### Run your migrations for the desired models
 
+Run:
+
+```shell
+rails generate migration AddDeletedAtToClients deleted_at:datetime
+```
+
+and now you have a migration
+
 ```ruby
-class AddDeletedAtToClient < ActiveRecord::Migration
-  def self.up
+class AddDeletedAtToClients < ActiveRecord::Migration
+  def change
     add_column :clients, :deleted_at, :datetime
   end
-
-  def self.down
-    remove_column :clients, :deleted_at
-  end
 end
 ```