Update README.md now that repo has moved to dart-lang/native

diff --git a/README.md b/README.md
index 3f2d0d8..2bcd24d 100644
--- a/README.md
+++ b/README.md

@@ -1,3 +1,9 @@
+# This package has moved!
+
+The package can now be found at https://github.com/dart-lang/native/tree/main/pkgs/ffigen
+
+-----
+
 [![pub package](https://img.shields.io/pub/v/ffigen.svg)](https://pub.dev/packages/ffigen)
 [![Build Status](https://github.com/dart-lang/ffigen/workflows/Dart%20CI/badge.svg)](https://github.com/dart-lang/ffigen/actions?query=workflow%3A"Dart+CI")
 [![Coverage Status](https://coveralls.io/repos/github/dart-lang/ffigen/badge.svg?branch=main)](https://coveralls.io/github/dart-lang/ffigen?branch=main)