Optimize the document for readability (#9730)

README.md

RELEASE.md

docs/azure-csi.md

docs/azure.md

docs/cloud.md

docs/equinix-metal.md

docs/etcd.md

docs/ha-mode.md

docs/integration.md

docs/kube-ovn.md

docs/kubernetes-reliability.md

docs/nodes.md

docs/offline-environment.md

docs/setting-up-your-first-cluster.md

docs/upgrades.md

docs/vars.md