Add PR Description Writer Skill

[DhanushNehru]

Create a skill that generates clear, well-structured pull request descriptions from code diffs. This is a companion to the existing git-commit-crafter skill.

What it should do

• Summarize what changed and why
• List files modified with brief explanations
• Highlight breaking changes, migration steps, and testing instructions
• Auto-detect if the PR is a feature, bugfix, refactor, or chore
• Generate a checklist: tests added, docs updated, screenshots attached

Skill File Location

skills/developer/pr-description-writer.md

Acceptance Criteria

• Follows SKILL_TEMPLATE.md
• At least 2 examples (feature PR, bugfix PR)
• Output includes a reviewer checklist
• Tips section with team-specific customization ideas

Difficulty: ⭐ (Beginner) — Great first contribution!