ChangeLog entry for partial SE-0143 adoption for Optional, Array, Dictionary.

Author: DougGregor

CHANGELOG.md

@@ -22,6 +22,13 @@ CHANGELOG
 Swift 4.1
 ---------
 
+* [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
+	can compare two values of type `[Int : [Int?]?]` with `==`), as well as use
+  various algorthims defined for `Equatable` element types, such as
+	`index(of:)`.
+
 * [SE-0157][] is implemented. Associated types can now declare "recursive"
 	constraints, which require that the associated type conform to the enclosing
 	protocol. The standard library protocols have been updated to make use of