Fix unavailable link in README.md (#1157)

Author: craiuconstantintiberiu

README.md

@@ -5,7 +5,7 @@
 ### v0.6.0 has introduced breaking changes. If you are upgrading from a previous version, follow the upgrade instructions outlined [in the release notes](https://github.com/mongodb/mongodb-kubernetes-operator/releases/tag/v0.6.0)
 
 
-This is a [Kubernetes Operator](https://coreos.com/operators/) which deploys MongoDB Community into Kubernetes clusters.
+This is a [Kubernetes Operator](https://kubernetes.io/docs/concepts/extend-kubernetes/operator/) which deploys MongoDB Community into Kubernetes clusters.
 
 If you are a MongoDB Enterprise customer, or need Enterprise features such as Backup, you can use the [MongoDB Enterprise Operator for Kubernetes](https://github.com/mongodb/mongodb-enterprise-kubernetes).