docs(readme): improve README structure and contributor onboarding (#28014)

[DanTheC0der]

Description

This PR improves the README structure and contributor onboarding guide for Cal.com, resolving issue #28014.

Changes Included

• Added structured Quick Start & Contributor Onboarding section.
• Added explicit prerequisite requirements (Node.js 20, pnpm 9, PostgreSQL/Docker).
• Added monorepo layout overview (apps/web, packages/prisma, packages/trpc).
• Added standard test (pnpm test) and lint (pnpm lint) verification instructions.

Resolves #28014

/claim #28014

[github-actions]

Welcome to Cal.diy, @DanTheC0der! Thanks for opening this pull request.

A few things to keep in mind:

• This is Cal.diy, not Cal.com. Cal.diy is a community-driven, fully open-source fork of Cal.com licensed under MIT. Your changes here will be part of Cal.diy — they will not be deployed to the Cal.com production app.
• Please review our Contributing Guidelines if you haven't already.
• Make sure your PR title follows the Conventional Commits format.

A maintainer will review your PR soon. Thanks for contributing!

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: ffc51398-2494-4b1e-a8f6-64645431eb5f

📥 Commits

Reviewing files that changed from the base of the PR and between 3894f37 and 34db63d.

📒 Files selected for processing (1)

• README.md

---

📝 Walkthrough

Walkthrough

README.md adds a “Quick Start & Contributor Onboarding” section with Node.js, pnpm, PostgreSQL or Docker prerequisites and local setup commands. It documents the monorepo layout through key application and package directories, and adds commands for running tests, linting, and builds.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR covers onboarding content, but it does not show key issue requirements like a TOC, architecture overview, or moving advanced docs out of README.	Add the missing README restructuring items from #28014, especially the table of contents, architecture overview, and doc migration details.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the README onboarding and structure updates in this PR.
Description check	✅ Passed	The description accurately describes the README onboarding and layout improvements.
Out of Scope Changes check	✅ Passed	The changes are confined to README onboarding and documentation updates, with no clear out-of-scope additions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[DanTheC0der]

/claim

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}