Add yarn version to setup steps

[JillieBeanSim]

Proposed changes

Adding yarn version to top level README for dev setup

Release Notes

Milestone: n/a

Changelog: n/a

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Updates to Documentation or Tests (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTOR GUIDANCE wiki
• PR title follows Conventional Commits Guidelines
• PR Description is included
• gif or screenshot is included if visual changes are made
• yarn workspace vscode-extension-for-zowe vscode:prepublish has been executed
• All checks have passed (DCO, Jenkins and Code Coverage)
• I have added unit test and it is passing
• I have added integration test and it is passing
• There is coverage for the code that I have added
• I have tested it manually and there are no regressions found
• I have added necessary documentation (if appropriate)
• Any PR dependencies have been merged and published (if appropriate)

Further comments

[traeok]

I'm wondering if we should update the Yarn link to point to the classic Yarn subdomain since we are still using v1? That way users do not have to click on the classic banner at the top to get to v1 instructions.

Suggested change

	- Install [Yarn](https://yarnpkg.com/getting-started/install) v1.22.19.
	- Install [Yarn](https://classic.yarnpkg.com/en/docs/install) v1.22.19.

[t1m0thyj]

Should we say to install Yarn Classic? I don't think the exact version number matters - if Yarn releases a 1.22.20 patch, we'd likely support it.

[JillieBeanSim]

Thanks all, changes pushed. feel free to push in updates to my PRs for Docs updates in the future 😉

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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[traeok]

Thanks @JillieBeanSim!