docs: add best practices guide for high-quality skills

[jmagly]

Summary

This PR adds a comprehensive best practices guide for creating high-quality Claude skills, addressing I2.2 from the roadmap ("Write best practices guide").

What's Included

docs/BEST_PRACTICES.md - A practical guide covering:

• Clear SKILL.md structure - Consistent sections, "When to Use" triggers
• Code examples - Why 5+ examples matter, what to include/avoid
• Prerequisites documentation - Patterns for documenting requirements
• Troubleshooting sections - Templates for common issues
• Reference organization - Category guidelines and navigation tables
• Quality workflow - Check targets, grade expectations
• Real-world example - Before/after showing improvement from Grade F to Grade A

Roadmap Alignment

This directly addresses:

• I2.2: Write best practices guide ✅

Style Matching

The guide follows existing documentation patterns from:

• BULLETPROOF_QUICKSTART.md (target audience header, time estimates, checklists)
• ENHANCEMENT.md (comparison tables, troubleshooting format)
• UPLOAD_GUIDE.md (step-by-step workflows, quick reference sections)

Contributing Project

This guide was contributed by the AI Writing Guide project, which integrates Skill Seekers for documentation-to-skill conversion. The best practices here are informed by research on production-grade agentic workflows.

Preview

Quick Checklist from the guide

Before uploading a skill, check:

• SKILL.md has clear "When to Use" triggers
• At least 5 code examples included
• Prerequisites documented (if any)
• Troubleshooting section present
• Quality score 90+ (Grade A)

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Thank you for building Skill Seekers - it's been valuable for our project! Happy to adjust anything based on feedback.