Update changelog for SE-0188

Author: natecook1000

CHANGELOG.md

@@ -22,6 +22,17 @@ CHANGELOG
 Swift 4.1
 ---------
 
+* [SE-0188][] 
+  
+  Index types for most standard library collections now conform to `Hashable`. 
+  These indices can now be used in key-path subscripts and hashed collections:
+  
+  ```swift
+  let s = "Hashable"
+  let p = \String.[s.startIndex]
+  s[keyPath: p] // "H"
+  ```
+
 * [SE-0143][] The standard library types `Optional`, `Array`, and
 	`Dictionary` now conform to the `Equatable` protocol when their element types
 	conform to `Equatable`. This allows the `==` operator to compose (e.g., one
@@ -6810,3 +6821,4 @@ Swift 1.0
 [SE-0184]: <https://github.com/apple/swift-evolution/blob/master/proposals/0184-unsafe-pointers-add-missing.md>
 [SE-0185]: <https://github.com/apple/swift-evolution/blob/master/proposals/0185-synthesize-equatable-hashable.md>
 [SE-0186]: <https://github.com/apple/swift-evolution/blob/master/proposals/0186-remove-ownership-keyword-support-in-protocols.md>
+[SE-0188]: <https://github.com/apple/swift-evolution/blob/master/proposals/0188-stdlib-index-types-hashable.md>