Add disclaimer to Kubelet Authentication proposal

Signed-off-by: Stefan Büringer [email protected]

Author: sbueringer

docs/proposals/20210222-kubelet-authentication.md

@@ -30,6 +30,8 @@ superseded-by:
 # Cluster API Kubelet Authentication
 
 
+**Note**: This proposal has not been implemented and should be carefully re-evaluated if it is still up-to-date before implementation.
+
 ## Table of Contents
 
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