Updated readme.

README.md

@@ -2,3 +2,21 @@ AsyncUnitTests
 ==============
 
 Helpers for async unit testing.
+
+Async-Aware Default Stub Behavior for Microsoft Fakes
+=====================================================
+
+The built-in default stub behavior for Microsoft Fakes will return `null` tasks from asynchronous methods. The [Nito.AsyncEx.UnitTests.MSFakes NuGet package](https://www.nuget.org/packages/Nito.AsyncEx.UnitTests.MSFakes/) provides the `AsyncAwareDefaultValueStubBehavior` type.
+
+Recommended usage is to apply the async-aware default stub behavior to all unit tests in a project:
+
+    [AssemblyInitialize]
+    public static void Initialize(TestContext context)
+    {
+        StubBehaviors.Current = new Nito.Async.UnitTests.AsyncAwareDefaultValueStubBehavior();
+    }
+
+However, it can be set on a test-by-test basis:
+
+    var stub = new Stub...;
+    stub.InstanceBehavior = new Nito.Async.UnitTests.AsyncAwareDefaultValueStubBehavior();