Update README

README.md

@@ -58,23 +58,24 @@ Documentation is generated by [jazzy](https://github.com/realm/jazzy).
 - [Playground](https://github.com/ra1028/DifferenceKit/blob/master/DifferenceKit.playground/Contents.swift)
 
 ### Example codes
-The type of the element that to take the differences must be conform to the `Differentiable` protocol:
+The type of the element that to take the differences must be conform to the `Differentiable` protocol. 
+The `identifier`'s type is determined generic by the associated type:
 ```swift
 struct User: Differentiable {
  let id: Int
  let name: String
 
- var differenceIdentifier: Int {
+ var identifier: Int {
  return id
  }
 
- func isUpdated(from source: User) -> Bool {
- return name != source.name
+ func isContentEqual(to source: User) -> Bool {
+ return name == source.name
  }
 }
 ```
 
-In the case of definition above, `id` uniquely identifies the element and get to know the user updated by comparing `name` of the elements in source and target.
+In the case of definition above, `id` uniquely identifies the element and get to know the user updated by comparing equality of `name` of the elements in source and target.
 
 There are default implementations of `Differentiable` for the types that conformed to `Equatable` or `Hashable`：
 ```swift