Adds docs/BEST_PRACTICES.md — a comprehensive guide for creating
high-quality Claude skills. Covers SKILL.md structure, code examples,
prerequisites, troubleshooting, quality targets, and a real-world
before/after example (Grade F to Grade A). Addresses roadmap item I2.2.
Based on PR #206 by @jmagly from the AI Writing Guide project.
Fixes applied: updated outdated CLI command, fixed broken doc links.
Co-authored-by: jmagly <jmagly@users.noreply.github.com>
