Document example of using cmd/helm as a library

[TerryHowe]

          Document example of using cmd/helm as a library

Originally posted by @TerryHowe in helm/helm#13617 (comment)

[scottrigby]

We also need the changes to be reflected on this page https://helm.sh/docs/community/developers/

[github-actions]

This issue has been marked as stale because it has been open for 90 days with no activity. This thread will be automatically closed in 30 days if no further activity occurs.