Update MetalLB README (#6140)

This updates MetalLB README as following
- Remove unnecessary markdown to read it easily on github
- Make words consistency (kubernetes, loadbalancer)
- Add change-required option

contrib/metallb/README.md

@@ -1,12 +1,19 @@
 # Deploy MetalLB into Kubespray/Kubernetes
-```
-MetalLB hooks into your Kubernetes cluster, and provides a network load-balancer implementation. In short, it allows you to create Kubernetes services of type “LoadBalancer” in clusters that don’t run on a cloud provider, and thus cannot simply hook into paid products to provide load-balancers.
-```
-This playbook aims to automate [this](https://metallb.universe.tf/concepts/layer2/). It deploys MetalLB into kubernetes and sets up a layer 2 loadbalancer.
+
+MetalLB hooks into your Kubernetes cluster, and provides a network load-balancer implementation.
+In short, it allows you to create Kubernetes services of type "LoadBalancer" in clusters that
+don't run on a cloud provider, and thus cannot simply hook into paid products to provide load-balancers.
+This playbook aims to automate [this](https://metallb.universe.tf/concepts/layer2/).
+It deploys MetalLB into Kubernetes and sets up a layer 2 load-balancer.
 
 ## Install
-```
-Defaults can be found in contrib/metallb/roles/provision/defaults/main.yml. You can override the defaults by copying the contents of this file to somewhere in inventory/mycluster/group_vars such as inventory/mycluster/groups_vars/k8s-cluster/addons.yml and making any adjustments as required.
 
+Defaults can be found in contrib/metallb/roles/provision/defaults/main.yml.
+You can override the defaults by copying the contents of this file to somewhere in inventory/mycluster/group_vars
+such as inventory/mycluster/groups_vars/k8s-cluster/addons.yml and making any adjustments as required.
+MetalLB allocates external IP addresses from this ip_range option, so you need to update this ip_range option
+at least for suiting your network environment.
+
+```
 ansible-playbook --ask-become -i inventory/sample/hosts.ini contrib/metallb/metallb.yml
 ```