This PR improves the developer experience for Windows users working with the WordPress development repository. It adds a Windows helper script (`start-windows.ps1`) and updates the README with clear instructions to avoid common issues.

# Summary
This pull request adds a Windows helper script (start-windows.ps1) to streamline the setup of the WordPress development environment on Windows machines.
Additionally, the README has been updated to include a dedicated "Windows Users" section with detailed guidance to address common npm warnings and errors that Windows developers encounter.

# Description of Changes

• Added start-windows.ps1 PowerShell script to:
  • Check if the repository root contains package.json
  • Install Node dependencies (npm install)
  • Build development files (npm run build:dev)
  • Start the WordPress development environment (npm run env:start)
• Updated README to:
  • Provide a clear "Windows Users" section
  • Document common npm warnings (Unknown user config) and how to fix them
  • Document ENOENT errors when package.json is not found
  • Provide step-by-step instructions for first-time setup, running WP-CLI commands, running tests, generating code coverage, and restarting/stopping/resetting the environment
  • Include guidance for Apple Silicon users with older MySQL/MariaDB container images

Trac ticket:
Trac ticket: https://core.trac.wordpress.org/ticket/64028