add cert prepare readme

[lingdie]

🤖 Generated by Copilot at 69ab747

Summary

📝☁️🌐

This pull request improves the documentation and usability of the sealos cloud cluster deployment. It supports alidns as a DNS provider and fixes the image source and argument order for the sealos run command in deploy/cloud/README.md.

Sing, O Muse, of the sealos cloud cluster, the mighty work of code
That guides the users to deploy their pods on Alibaba's abode
And how they learned to use alidns, the swift and clever tool
That links their names with IP addresses, following the rule

Walkthrough

• Add instructions for getting a TLS certificate with alidns and base64 encoding it (link)
• Update image name and data fields for tls-secret.yaml file (link, link)
• Update image name and argument order for sealos run command in deploy/cloud/README.md (link)