Update quickstart.md

[mfreeman451]

v4-alpha doesnt exist

Description of the change:

Motivation for the change:

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• Add or update relevant sections of the docs website in website/content/en/docs

[OchiengEd]

Thank you for your pull request, noticed your commit is not signed. This will result in a failure in the checks, so consider signing your commit.

In addition, this is a duplicate of #6727. So it could end up being closed prior to being merged.

@mfreeman451 See the docs for how to go about it.