Update CHANGELOG.md for pack element captures

Author: slavapestov

CHANGELOG.md

@@ -5,6 +5,20 @@
 
 ## Swift 6.0
 
+* Closures can now appear in pack expansion expressions, which allows you to
+  construct a parameter pack of closures where each closure captures the
+  corresponding element of some other parameter pack. For example:
+
+  ```swift
+  struct Manager<each T> {
+    let fn: (repeat () -> (each T))
+
+    init(_ t: repeat each T) {
+      fn = (repeat { each t })
+    }
+  }
+  ```
+
 * [SE-0431][]:
   You can now require a function value to carry its actor isolation
   dynamically in a way that can be directly read by clients: