[doc] Update Venia setup doc

[jcalcaben]

Description

Updates the Venia setup docs.
Specifically, it switches step 3 & 4 to align with what the project recommends when running the CLI commands.

Related Issue

Closes #ISSUE_NUMBER.

Acceptance

@awilcoxa

Verification Stakeholders

@awilcoxa

Specification

Verification Steps

1. Navigate to pwa-devdocs
2. Run linter on changed file: npm run lint src/venia-pwa-concept/setup/index.md
3. Verify no linting errors.
4. Run HTML preview server: npm run develop
5. Navigate to /venia/pwa-concept/setup page.
6. Follow steps on a fresh local instance of the repo
7. Verify steps result in a running instance of Venia.

Screenshots / Screen Captures (if appropriate)

Checklist

• I have updated the documentation accordingly, if necessary.
• I have added tests to cover my changes, if necessary.

[PWAStudioBot]

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[cherdman]

Ship it!