Update README.md before archiving (#94)

README.md

diff --git a/README.md b/README.md
index 212c48e..d7b0f81 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,6 @@
+> [!IMPORTANT]  
+> This repo has moved to https://github.com/dart-lang/core/tree/main/pkgs/typed_data
+
 [![Dart CI](https://github.com/dart-lang/typed_data/actions/workflows/test-package.yml/badge.svg)](https://github.com/dart-lang/typed_data/actions/workflows/test-package.yml)
 [![pub package](https://img.shields.io/pub/v/typed_data.svg)](https://pub.dev/packages/typed_data)
 [![package publisher](https://img.shields.io/pub/publisher/typed_data.svg)](https://pub.dev/packages/typed_data/publisher)