docs: Make it clear that this repo is inactive (#367)

* Make it clear that this repo is inactive

The repo admin should also mark the repo as "inactive" in Github settings

* spelling

README.md

@@ -1,6 +1,14 @@
 [![codecov](https://codecov.io/gh/argoproj-labs/argocd-notifications/branch/master/graph/badge.svg)](https://codecov.io/gh/argoproj-labs/argocd-notifications)
 
-# Argo CD Notifications
+# Argo CD Notifications is now part of Argo CD
+
+**This project has moved to the main Argo CD repository**
+
+This repository is no longer active. The Argo CD notifications project is now merged with [Argo CD](https://github.com/argoproj/argo-cd) and released along with it.
+Further development will happen there.
+See [https://argo-cd.readthedocs.io/en/latest/operator-manual/notifications/](https://argo-cd.readthedocs.io/en/latest/operator-manual/notifications/) for more details.
+
+# Argo CD Notifications - OLD README
 
 Argo CD Notifications continuously monitors Argo CD applications and provides a flexible way to notify
 users about important changes in the applications state. The project includes a bundle of useful
@@ -17,6 +25,6 @@ like [bitnami-labs/kubewatch](https://github.com/bitnami-labs/kubewatch) and
 [argo-kube-notifier](https://github.com/argoproj-labs/argo-kube-notifier). The advantage of Argo CD Notifications is that
 it is focused on Argo CD use cases and ultimately provides a better user experience.
 
-# Documentation
+# Old Documentation
 
 Go to the complete [documentation](https://argoproj-labs.github.io/argocd-notifications/) to learn more.