Add deprecation warning

* to NOTES.txt
* to fluxctl install

Let new users know as soon as they start using Flux that this version is
going to be deprecated.

Signed-off-by: Kingdon Barrett <kingdon@weave.works>

chart/flux/templates/NOTES.txt

@@ -8,3 +8,12 @@ and running:
 
   fluxctl identity --k8s-fwd-ns {{ .Release.Namespace }}
 
+---
+
+**Flux v1 is deprecated, please upgrade to v2 as soon as possible!**
+
+New users of Flux can Get Started here:
+https://fluxcd.io/docs/get-started/
+
+Existing users can upgrade using the Migration Guide:
+https://fluxcd.io/docs/migration/

cmd/fluxctl/install_cmd.go

@@ -61,6 +61,16 @@ fluxctl install --git-url 'git@github.com:<your username>/flux-get-started' --gi
 }
 
 func (opts *installOpts) RunE(cmd *cobra.Command, args []string) error {
+	fmt.Fprintf(os.Stderr, `**Flux v1 is deprecated, please upgrade to v2 as soon as possible!**
+
+New users of Flux can Get Started here:
+https://fluxcd.io/docs/get-started/
+
+Existing users can upgrade using the Migration Guide:
+https://fluxcd.io/docs/migration/
+
+`)
+
 	if len(args) != 0 {
 		return errorWantedNoArgs
 	}