Add comment to clarify

Add comment as requested in peer review.

Author: martincostello

src/Polly.Core/Utils/TimeProviderExtensions.cs

@@ -25,7 +25,11 @@ public static Task DelayAsync(this TimeProvider timeProvider, TimeSpan delay, Re
 
         if (context.IsSynchronous)
         {
-#pragma warning disable CA1849 // For synchronous scenarios we want to return completed task
+#pragma warning disable CA1849
+            // For synchronous scenarios we want to return a completed task. We avoid
+            // the use of Thread.Sleep() here because it is not cancellable and to
+            // simplify the code. Sync-over-async is not a concern here because it
+            // only applies in the case of a reilience event and not on the hot path.
             timeProvider.Delay(delay, context.CancellationToken).GetAwaiter().GetResult();
 #pragma warning restore CA1849