README.md in acfs-0.28.0.1.b249 vs README.md in acfs-0.28.0.1.b253

@@ -128,9 +128,10 @@
 
 Acfs.run # Will request `http://users.myapp.org/users?age=24`
 
 @user # Contains the first user object returned by the index action
 ```
+If no object can be found, `.find_by` will return `nil`. The optional callback will then be called with `nil` as parameter. Use `.find_by!` to raise an `Acfs::ResourceNotFound` exception if no object can be found. `.find_by!` will only invoke the optional callback if an object was successfully loaded.
 
 Acfs has basic update support using `PUT` requests:
 
 ```ruby
 @user = User.find 5