Update README.md

Author: ntkme

README.md

@@ -1 +1,15 @@
-# dart
+# Dart
+
+[![schedule](https://github.com/dart-android/dart/actions/workflows/schedule.yml/badge.svg)](https://github.com/dart-android/dart/actions/workflows/schedule.yml)
+
+## Download URLs
+
+You can download tar.gz files for any channel.
+
+### Stable, beta, and dev channel URL scheme
+
+Stable, beta, and dev channel releases are available at URLs like the following:
+
+```
+https://github.com/dart-android/dart/releases/download/<version>/dartsdk-<platform>-<architecture>-release.tar.gz
+```