docs: Add note about --cni=cilium flag

From minikube v1.12.1+, the flag passed to `minikube start` command
will deploy quick-install.yaml automatically. However, it currently installs
v1.8 by default so add a note regarding this.

Signed-off-by: Aditi Ghag <aditi@cilium.io>

Documentation/gettingstarted/k8s-install-default.rst

@@ -99,6 +99,12 @@ to create a Kubernetes cluster locally or using a managed Kubernetes service:
 
           minikube start --network-plugin=cni
 
+    .. note::
+
+       From minikube v1.12.1+, cilium networking plugin can be enabled directly with
+       ``--cni=cilium`` parameter in ``minikube start`` command. However, this may not
+       install the latest version of cilium.
+
 Install the Cilium CLI
 ======================