Add release notes for SE-0329: Clock, Instant, and Duration

Author: phausler

CHANGELOG.md

@@ -5,6 +5,25 @@ _**Note:** This is in reverse chronological order, so newer entries are added to
 
 ## Swift 5.7
 
+* [SE-0329][]:
+  New types representing time and clocks were introduced. This includes a protocol `Clock` defining clocks which allow for defining a concept of now and a way to wake up after a given instant. Additionally a new protocol `InstantProtocol` for defining instants in time was added. Furthermore a new protocol `DurationProtocol` was added to define an elapsed duration between two given `InstantProtocol` types. Most commonly the `Clock` types for general use are the `SuspendingClock` and `ContinuousClock` which represent the most fundamental clocks for the system. The `SuspendingClock` type does not progress while the machine is suspended whereas the `ContinuousClock` progresses no matter the state of the machine. 
+
+  ```swift
+    func delayedHello() async throws {
+      try await Task.sleep(until: .now + .milliseconds(123), clock: .continuous)
+      print("hello delayed world")
+    }
+  ```
+
+  `Clock` also has methods to measure the elapsed duration of the execution of work. In the case of the `SuspendingClock` and `ContinuousClock` this measures with high resolution and is suitable for benchmarks.
+
+  ```swift
+  let clock = ContinuousClock()
+  let elapsed = clock.measure {
+    someLongRunningWork()
+  }
+  ```
+
 * References to `optional` methods on a protocol metatype, as well as references to dynamically looked up methods on the `AnyObject` metatype are now supported. These references always have the type of a function that accepts a single argument and returns an optional value of function type:
 
   ```swift