docs: improve contributor experience with setup guide and enhanced gitignore

[surajsk2003]

Why

Improve the onboarding experience for new contributors by providing clear setup instructions and better project hygiene.

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What's Being Changed

Enhanced README.md

• Added Prerequisites section with Node.js version requirements
• Added Quick Start section with step-by-step installation instructions
• Added Available Scripts section explaining common npm commands

Improved .gitignore

• Included a comprehensive list of common files and directories to ignore
• Added OS-specific files (.DS_Store, Thumbs.db, etc.)
• Ignored build artifacts and cache directories

Created CONTRIBUTING.md

• Included a simple setup guide for new contributors
• Added suggestions for easy first contributions
• Linked to detailed documentation and community guidelines

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Checklist

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR
  In most cases, the author can be the SME. For open source contributions, GitHub staff may review.
• The changes in this PR meet the Docs content fundamentals.
• All CI checks are passing and the changes look good in the review environment.

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Let me know if any adjustments are required. Happy to improve the experience for future contributors!

[welcome]

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[github-actions]

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[Copilot]

Pull Request Overview

This PR improves the onboarding experience by enhancing the main README with clear setup instructions and introducing a dedicated CONTRIBUTING guide.

• Expanded README with prerequisites, quick start steps, and script explanations
• Added a CONTRIBUTING.md with first-time setup, branch workflow, and easy-entry tasks

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
README.md	Added Prerequisites, Quick Start, and Available Scripts sections
CONTRIBUTING.md	New contributor guide covering setup, change workflow, and help resources

Comments suppressed due to low confidence (4)

README.md:10

• Use an asterisk (*) instead of a hyphen for bullet lists to comply with the repository's Markdown style guidelines.

- **Node.js**: Version 20 or 22 (see [engines](package.json) in package.json)

README.md:37

• Switch this list item to use an asterisk (*) instead of a hyphen for consistency with the project content guidelines.

- `npm run dev` - Start development server with English content only

CONTRIBUTING.md:1

• Replace the hardcoded product name “GitHub Docs” with the corresponding Liquid variable (e.g. {% data variables.product.github %}) to ensure variable-driven consistency across content.

# Contributing to GitHub Docs

CONTRIBUTING.md:54

• Use an asterisk (*) for this bullet list item instead of a hyphen to align with the Markdown bulleted list convention in our content guidelines.

- Fix typos in documentation