Feat: Updated README for Prerequisites before setting-up Cluster Autoscaler.

[nileshgadgi]

Don't merge this before this PR.

PR-#48 should be merged in top priority

what

• Described prerequisites before Cluster autoscaler setup in kubernetes cluster.
• Adedd tags in kubernetes node groups as far as cluster autoscaler is true in complete example.

why

• ASG tagging is required to enable Discovery for Cluster autoscaler.
• Auto-discovery finds ASGs tags as below and automatically manages them based on the min and max size specified in the ASG.

references

• https://artifacthub.io/packages/helm/cluster-autoscaler/cluster-autoscaler