docs: update README with cross-platform setup and formatting

[Tausif-11]

Description

This PR enhances and restructures the README.md to improve clarity and onboarding for new contributors, especially those working on Windows environments.

Key Changes

• Cross-Platform Instructions: Added dedicated PowerShell setup commands for Windows alongside standard Bash commands for macOS/Linux.
• Environment Configuration: Included explicit commands for copying .env.local.sample to .env.local for both Bash and PowerShell.
• Typo Fixes: Corrected environment file path references from env.local to .env.local.
• Improved Readability: Restructured setup options into clear Docker vs. Native workflows, added a Table of Contents, and updated code block formatting for linting/formatting instructions.

Checklist

• Tested Markdown rendering to ensure clean structure and formatting.
• Verified PowerShell and Bash commands.
• Followed repository contribution guidelines (single-focused PR).