Restructure the skills folder (onnx#346)

According to Github requirements

Signed-off-by: Justin Chu <justinchuby@users.noreply.github.com>

Author: justinchuby

.github/skills/README.md

@@ -4,7 +4,7 @@ This directory contains specialized skills for AI agents working with the ONNX I
 
 ## Available Skills
 
-### [Pass Writing](./pass-writing.md)
+### [Pass Writing](./pass-writing/SKILL.md)
 
 Comprehensive guide for creating transformation passes in ONNX IR. This skill covers:
 
@@ -31,7 +31,8 @@ These skills are designed to be used by AI agents to improve code quality and co
 
 When adding new skills:
 
-1. Create a descriptive markdown file in this directory
-2. Update this README with a brief description of the new skill
-3. Include comprehensive examples from the codebase
-4. Document both what to do and what to avoid
+1. Create a new directory under `skills/` with a lowercase, hyphenated name (e.g., `webapp-testing`)
+2. Add a `SKILL.md` file inside the directory with the skill content
+3. Update this README with a brief description of the new skill
+4. Include comprehensive examples from the codebase
+5. Document both what to do and what to avoid

.github/skills/pass-writing.md .github/skills/pass-writing/SKILL.md.github/skills/pass-writing.md renamed to .github/skills/pass-writing/SKILL.md

@@ -1,6 +1,7 @@
-# ONNX IR Pass Writing Skill
-
-This skill provides comprehensive guidance for creating transformation passes in the ONNX IR project. It encapsulates best practices, conventions, and patterns derived from existing passes in `onnx_ir/passes/common/`.
+---
+name: pass-writing
+description: Comprehensive guidance for creating transformation passes in the ONNX IR project. It encapsulates best practices, conventions, and patterns derived from existing passes in `onnx_ir/passes/common/`.
+---
 
 ## Overview