Fix kube config permission warnings

[barbarebelge]

skaffold-helm-tutorial/chapters/03-install-k3s.md

Lines 115 to 125 in b58b7c6

	### Configuring: kube config
	Once K3s has finished startup, a file `/etc/rancher/k3s/k3s.yaml` will be created with configuration and credentials for connecting to the kubernetes cluster. This configuration is needed by all our client tools (`helm`, `kubectl`, `k9s`, ...) to make a succesfull connection to kubernetes.
	The client tools typically look for a client configuration in `.kube/config` in your homedir, so let's copy the file there. We need to use sudo because by default the file is only readable by root.
	```shell
	mkdir -p $HOME/.kube
	sudo cat /etc/rancher/k3s/k3s.yaml > $HOME/.kube/config
	```
	Sometimes you will have multiple clusters to manage. You will then have multiple config files. You can use the `KUBECONFIG` environment variable to tell the client tools which config file they should use. Alternatively, you can merge multiple kubeconfigs in one file. [This guide](https://stackoverflow.com/questions/46184125/how-to-merge-kubectl-config-file-with-kube-config) explains how.

In this section, might be useful to mention that one should set permissions properly on $HOME/.kube/config to avoid warnings when calling helm or kubectl.

Here is the command to avoid this:

chmod o-r $HOME/.kube/config && chmod g-r $HOME/.kube/config