Docs: update GitHub Discussions links

[coliff]

Description

Update GitHub Discussions link in introduction.mdx

Motivation & Context

Shorter and saves a HTTP redirect

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-42049--twbs-bootstrap.netlify.app/

[Copilot]

Pull request overview

Updates the GitHub Discussions URL in the “Community” section of the Getting Started introduction to use the direct org-level Discussions link (avoiding an extra redirect).

Changes:

• Replace the repository Discussions URL with the organization Discussions URL in the docs.

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[julien-deramond]

Thanks for the PR, @coliff 🙏
I made a few tweaks to other GitHub Discussions links in the repo while reviewing this. LGTM overall.
Putting this on hold for now until we decide how to handle main vs v6-dev (rebases / branch renaming).