Add License section to ADS extension README (#654)

extensions/azdata-sanddance/README.md

@@ -28,3 +28,7 @@ Major upgrade to layout engine
 ### 1.0.0
 
 Initial release of azdata-sanddance
+
+## License
+
+This extension is licensed under the [MIT License](https://github.com/microsoft/SandDance/blob/main/extensions/azdata-sanddance/LICENSE).