Update the helm readme

[jseldess]

Jesse Seldess (jseldess) commented:

Update the upgrade and scaling instructions to use helm commands, like our docs: https://github.com/helm/charts/tree/master/stable/cockroachdb

Jira Issue: DOC-292

[exalate-issue-sync[bot]]

Jesse Seldess (jseldess) commented: Is this still a need, Ryan Kuo?

[github-actions[bot]]

We have marked this issue as stale because it has been inactive for 18 months. If this issue is still relevant, removing the stale label or adding a comment will keep it active. Otherwise, we'll close it in 10 days to keep the issue queue tidy. Thank you for your contribution to CockroachDB docs!