Update README.md

Mention that project has moved into the sdk repository.

README.md

diff --git a/README.md b/README.md
index 8239a3d..77002bb 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,10 @@
+Moved
+=====
+
+This has moved into the [Dart SDK repository](github.com/dart-lang/sdk).
+
+This repository is not kept up-to-date.
+
 Dart Kernel
 ===========
 **Dart Kernel** is a small high-level language derived from Dart.