Add guide to set up kubectl

[deliahu]

Description

Something along the lines of:

You can install eksctl by following their instructions, install kubectl by following their instructions, and then run the command eksctl utils write-kubeconfig --cluster=<cluster_name> --region=<region> (for example: eksctl utils write-kubeconfig --cluster=cortex --region=us-west-2). After that, kubectl commands should work as expected.