Added deprecated notice to commands with direct replacement (#612)

README.md

@@ -7,6 +7,8 @@
 
 `gsctl` is the cross-platform command line utility to manage your Kubernetes clusters at Giant Swarm.
 
+> gsctl and the [REST API](https://docs.giantswarm.io/ui-api/rest-api/) are being phased out. We don't have an end-of-life date yet. However, we recommend to familiarize yourself with our [Management API](https://docs.giantswarm.io/ui-api/management-api/) and the [kubectl gs](https://docs.giantswarm.io/ui-api/kubectl-gs/) plugin as a future-proof replacement.
+
 ## Usage
 
 Call `gsctl` without any arguments to get an overview on commands. Some usage examples:

commands/create/cluster/command.go

@@ -201,6 +201,10 @@ suppress the creation of the default node pool by setting the flag
   gsctl create cluster \
     --owner acme \
     --create-default-nodepool=false
+`,
+		Deprecated: `gsctl is being phased out in favour of our 'kubectl gs' plugin.
+We recommened you familiarize yourself with the 'kubectl gs template' command as a replacement for this.
+For more details see: https://docs.giantswarm.io/ui-api/kubectl-gs/template-cluster/
 `,
 		PreRun: printValidation,
 		Run:    printResult,

commands/create/nodepool/command.go

@@ -129,6 +129,11 @@ Examples:
   By setting this value to '-1', the maximum price will be set
   to the on-demand price of the instance.
 
+`,
+
+		Deprecated: `gsctl is being phased out in favour of our 'kubectl gs' plugin.
+We recommened you familiarize yourself with the 'kubectl gs template' command as a replacement for this.
+For more details see: https://docs.giantswarm.io/ui-api/kubectl-gs/template-nodepool/
 `,
 
 		// PreRun checks a few general things, like authentication.

commands/list/clusters/command.go

@@ -46,6 +46,10 @@ Examples:
   gsctl list clusters --selector environment=testing
 
   gsctl list clusters --sort org
+`,
+		Deprecated: `gsctl is being phased out in favour of our 'kubectl gs' plugin.
+We recommened you familiarize yourself with the 'kubectl gs get' command as a replacement for this.
+For more details see: https://docs.giantswarm.io/ui-api/kubectl-gs/get-clusters/
 `,
 		PreRun: printValidation,
 		Run:    printResult,