Add README for change note validation test usage

Co-authored-by: Napalys <11835209+Napalys@users.noreply.github.com>

README-CHANGE-NOTE-VALIDATION.md

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+# Change Note Validation Test Script
+
+This directory contains a comprehensive test script to validate CodeQL change note file formats and understand the exact requirements for CodeQL pack release validation.
+
+## Quick Start
+
+```bash
+# Run the validation test
+python3 test-change-notes-validation.py
+```
+
+## What This Test Does
+
+The test script helps debug and understand:
+
+1. **File naming patterns** - What formats are accepted
+2. **YAML frontmatter requirements** - What fields are required
+3. **Content format validation** - What content structures work
+4. **Category validation** - Different categories for library vs query packs
+5. **Specific issue debugging** - Why certain files fail validation
+
+## Test Coverage
+
+The script creates and validates 15 different test files covering:
+
+- ✅ Valid change notes with proper YAML frontmatter
+- ✅ Valid change notes with different categories
+- ✅ Valid change notes with proper date formats
+- ❌ Invalid change notes without frontmatter
+- ❌ Invalid change notes with malformed YAML
+- ❌ Invalid change notes with wrong categories
+- ❌ Invalid change notes with empty content
+- ❌ Invalid change notes with wrong filename formats
+- ❌ Invalid change notes with invalid dates
+
+## Sample Valid Change Note
+
+```markdown
+---
+category: minorAnalysis
+---
+* Added taint flow model for new function to improve security analysis.
+```
+
+## Common Issues and Solutions
+
+### Issue: Wrong Filename Format
+**Problem:** `2025-07-08.md` (missing description)
+**Solution:** `2025-07-08-description.md`
+
+### Issue: Missing YAML Frontmatter
+**Problem:** File starts with content directly
+**Solution:** Add YAML frontmatter with `---` delimiters
+
+### Issue: Invalid Category
+**Problem:** Using wrong category for pack type
+**Solution:** Use valid categories (see documentation)
+
+### Issue: Empty Content
+**Problem:** No content after YAML frontmatter
+**Solution:** Add descriptive content with bullet points
+
+## Files Created
+
+- `test-change-notes-validation.py` - Main test script
+- `CHANGE_NOTE_VALIDATION_RESULTS.md` - Detailed documentation
+- `actions/ql/lib/change-notes/2025-07-08-test-validation.md` - Sample valid file
+
+## Usage Examples
+
+```bash
+# Run full validation test
+python3 test-change-notes-validation.py
+
+# Test a specific file
+python3 -c "
+from test-change-notes-validation import ChangeNoteValidator
+validator = ChangeNoteValidator()
+errors = validator.validate_file('path/to/your/file.md', 'library_pack')
+print('✅ Valid' if not errors else '❌ Invalid: ' + ', '.join(errors))
+"
+```
+
+## Understanding the Output
+
+The script provides clear validation results:
+- ✅ **VALIDATION PASSED** - File follows all requirements
+- ❌ **VALIDATION FAILED** - Lists specific issues to fix
+
+## Pack Types
+
+The script validates for both pack types:
+- **Library packs** - Use categories: breaking, deprecated, feature, majorAnalysis, minorAnalysis, fix
+- **Query packs** - Use categories: breaking, deprecated, newQuery, queryMetadata, majorAnalysis, minorAnalysis, fix
+
+## Next Steps
+
+1. Run the test to understand current validation state
+2. Fix any failing change notes based on the error messages
+3. Use the sample files as templates for new change notes
+4. Run `codeql pack release --dry-run` to validate with actual CodeQL CLI