Calculate Kenya payroll deductions - PAYE, SHIF, NSSF, Housing Levy with accurate 2024/2025 rates
- Added detailed documentation in SKILL.md covering all 2024/2025 Kenya payroll tax rates and calculation methods. - Clarified usage examples for calculating PAYE, SHIF (new 2.75% rate), NSSF (with new limits), and Housing Levy. - Listed all supported tax reliefs and provided updated API function reference.