doc: Add referal to quick install and GSG in k8s install guide
doc: Add referal to quick install and GSG in k8s install guide

Make sure readers landing on the k8s install guide page are aware of the
quick install and getting started with minikube options.

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

michi-covalent/cilium,cilium-team/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,eloycoto/cilium,scanf/cilium,scanf/cilium,scanf/cilium,scanf/cilium,cilium/cilium,eloycoto/cilium,eloycoto/cilium,tklauser/cilium,cilium/cilium,scanf/cilium,eloycoto/cilium,cilium-team/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,michi-covalent/cilium,scanf/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,scanf/cilium,eloycoto/cilium,tgraf/cilium,tgraf/cilium,eloycoto/cilium,eloycoto/cilium,tklauser/cilium,cilium/cilium