docs: improve README structure and clarity

[devin-ai-integration]

docs: improve README structure and clarity

Summary

Full rewrite of the README to improve structure, readability, and completeness. All content remains in English. Key changes:

• Table of Contents: Added TOC for quick navigation between sections
• "How It Works" section: Added architecture diagram (Browser → Nginx → Laravel App) to explain the plugin visually
• "Requirements" section: Explicitly listed prerequisites
• Environment variables as table: Changed from nested list format to a table for better scannability
• Custom Domain example: Added concrete .env and /etc/hosts configuration example for using a custom domain
• Certificate import as table: Reformatted browser/OS instructions into a table; added Windows steps
• Troubleshooting section: Added guidance for port conflicts, certificate regeneration, and HTTP URL generation issues
• Simplified AppServiceProvider example: Replaced full class definition with just the relevant boot() method snippet
• Install command note: Added note explaining compose.yaml support and skip behavior when nginx service already exists
• License section: Added explicit link to LICENSE file
• Minor cleanup: Removed emoji from title, improved wording throughout

Updates Since Last Revision

• Rewrote the entire README from Japanese back to English per user request. All structural improvements (TOC, tables, troubleshooting, etc.) are preserved.

Review & Testing Checklist for Human

• Table of Contents anchor links: Verify that all TOC links (e.g. #how-it-works, #trust-the-certificate-optional) render and navigate correctly on GitHub
• New content accuracy: The Custom Domain example and Troubleshooting sections contain new guidance not present in the original README — verify these match actual plugin behavior
• AppServiceProvider code snippet: The example was simplified to show only the boot() method instead of the full class — confirm this is clear enough for your target audience

Notes

• Link to Devin run: https://app.devin.ai/sessions/0f1fdea627af44a39188c615b38bb0bd
• Requested by: @ryoluo

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