Add "What is a Cursor Skill?" section to README

[DeanKelly751]

Summary

The README jumps straight into listing skills without explaining what a Cursor skill is. New users unfamiliar with Cursor's skill system will be confused.

Proposed Solution

Add a short section near the top of the README that explains:

• What a Cursor agent skill is
• How skills are discovered and triggered
• Where to place skill files (.cursor/skills/ or ~/.cursor/skills/)

Acceptance Criteria

• README includes a "What is a Cursor Skill?" section before the skills list
• Explanation is concise (3-5 sentences max)