Write installation instructions for Kubernetes

## Overview
Write the procedure [Installation as part of Kubernetes installation](install/#installation-as-part-of-kubernetes-installation), or link to Kubernetes documentation that includes etcd installation as backstore. Explain and fill in (on the etcd docs page) any gaps in the procedure.

Audience: Kubernetes Operator

Type: Task

The existing documentation might contain helpful source material that you can pull into this doc change. See recommendations for the existing (at the time of the CNCF tech doc analysis) etcd technical documentation pages:
https://github.com/cncf/techdocs/blob/main/assessments/0010-etcd/etcd-implementation.md/#general-reorganization

## 🎤 Context

This issue tracks recommended changes resulting from an analysis of the etcd documentation commissioned by CNCF. The analysis and supporting documents are here: https://github.com/cncf/techdocs/tree/main/assessments/0010-etcd/

## ✌️ Possible Implementation

Related material in the current doc:
- https://github.com/etcd-io/website/tree/main/content/en/docs/v3.5/install.md