message: docs: add release announcement URL
diff: ### Release Highlights & Update instructions
  -To learn about the release highlights and our new CLI-powered update workflow for your projects please check out the [v7 release announcement](https://blog.angular.io/TODO).
  +To learn about the release highlights and our new CLI-powered update workflow for your projects please check out the [v7 release announcement](https://blog.angular.io/version-7-of-angular-cli-prompts-virtual-scroll-drag-and-drop-and-more-c594e22e7b8c).
  ### Dependency updates
  