[DOC] Explain where to download kubectl

Some people weren't sure on which machine we have to install it.

Issue-ID: OOM-2061
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>
Change-Id: Ib46ac2211a716e04ce5b8d9394264bb7fd34a42c
diff --git a/docs/oom_setup_kubernetes_rancher.rst b/docs/oom_setup_kubernetes_rancher.rst
index 19ac52b..1b5d6d1 100644
--- a/docs/oom_setup_kubernetes_rancher.rst
+++ b/docs/oom_setup_kubernetes_rancher.rst
@@ -344,6 +344,12 @@
 https://storage.googleapis.com/kubernetes-release/release/v1.15.2/bin/linux/amd64/kubectl
 https://storage.googleapis.com/kubernetes-release/release/v1.15.2/bin/darwin/amd64/kubectl
 
+You only need to install kubectl where you'll launch kubernetes command. This
+can be any machines of the kubernetes cluster or a machine that has IP access
+to the APIs.
+Usually, we use the first controller as it has also access to internal
+Kubernetes services, which can be convenient.
+
 Validate deployment
 -------------------