add a preview note for all non-bootstrap commands

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

cmd/flux/create_receiver.go

@@ -37,7 +37,7 @@ import (
 var createReceiverCmd = &cobra.Command{
 	Use:   "receiver [name]",
 	Short: "Create or update a Receiver resource",
-	Long:  "The create receiver command generates a Receiver resource.",
+	Long:  `The create receiver command generates a Receiver resource.`,
 	Example: `  # Create a Receiver
   flux create receiver github-receiver \
 	--type github \