diff --git a/docs/08-bootstrapping-kubernetes-controllers.md b/docs/08-bootstrapping-kubernetes-controllers.md
index e102e34..263f5d5 100644
--- a/docs/08-bootstrapping-kubernetes-controllers.md
+++ b/docs/08-bootstrapping-kubernetes-controllers.md
@@ -30,6 +30,8 @@ wget -q --show-progress --https-only --timestamping \
   "https://storage.googleapis.com/kubernetes-release/release/v1.13.0/bin/linux/amd64/kubectl"
 ```
 
+Reference: https://kubernetes.io/docs/setup/release/#server-binaries
+
 Install the Kubernetes binaries:
 
 ```