docs: update README with GA for Copilot (#1124)

README.md

@@ -1,9 +1,9 @@
-__✨ The [AWS Copilot CLI](https://github.com/aws/copilot-cli) is now in preview: a new way to build, release and operate your container apps on ECS and Fargate__
+__✨ The [AWS Copilot CLI](https://github.com/aws/copilot-cli) is now in Generally Available! The CLI makes it easy to build, release and operate your container apps on Amazon ECS and AWS Fargate.__
 
 <details>
 <summary>Learn more about the AWS Copilot CLI</summary>
 
-The [AWS Copilot CLI](https://github.com/aws/copilot-cli) is a brand new CLI focused on the full developer experience of building, deploying and operating your containerized apps. From helping manage all of your infrastructure, to setting up CD Pipelines, `copilot` is here to help. [AWS Copilot](https://github.com/aws/copilot-cli) is in preview and quite different from the ECS CLI, but we'd love your feedback! To learn more about AWS Copilot, check out the [wiki](https://github.com/aws/copilot-cli/wiki).
+The [AWS Copilot CLI](https://github.com/aws/copilot-cli) is a CLI focused on the full developer experience of building, deploying and operating your containerized apps. From helping manage all of your infrastructure, to setting up CD Pipelines, `copilot` is here to help. To learn more about AWS Copilot, check out the [documentation](https://aws.github.io/copilot-cli/).
 </details>