docs: add coverage badges and onboarding guide

- Add test coverage (100%) and type coverage (100%) badges to README
- Create concise onboarding guide for new contributors
- Guide covers: setup, structure, PURL basics, development workflow

Critical information first with visual structure.

Author: jdalton

README.md

@@ -2,6 +2,8 @@
 
 [![Socket Badge](https://socket.dev/api/badge/npm/package/@socketregistry/packageurl-js)](https://socket.dev/npm/package/@socketregistry/packageurl-js)
 [![CI - @socketregistry/packageurl-js](https://github.com/SocketDev/socket-packageurl-js/actions/workflows/ci.yml/badge.svg)](https://github.com/SocketDev/socket-packageurl-js/actions/workflows/ci.yml)
+![Test Coverage](https://img.shields.io/badge/test--coverage-100%25-brightgreen)
+![Type Coverage](https://img.shields.io/badge/type--coverage-100%25-brightgreen)
 
 [![Follow @SocketSecurity](https://img.shields.io/twitter/follow/SocketSecurity?style=social)](https://twitter.com/SocketSecurity)
 [![Follow @socket.dev on Bluesky](https://img.shields.io/badge/Follow-@socket.dev-1DA1F2?style=social&logo=bluesky)](https://bsky.app/profile/socket.dev)

docs/onboarding-guide.md

@@ -0,0 +1,154 @@
+# Onboarding Guide
+
+**New Contributor Quickstart** — Get started with Package URL development in 5 minutes.
+
+---
+
+## 📋 Prerequisites
+
+```
+Required:
+ ✓ Node.js 20+ (LTS recommended)
+ ✓ pnpm 9+
+ ✓ Git
+```
+
+---
+
+## 🚀 Quick Start
+
+### 1. Clone & Setup
+
+```bash
+# Clone
+git clone https://github.com/SocketDev/socket-packageurl-js.git
+cd socket-packageurl-js
+
+# Install & verify
+pnpm install
+pnpm test
+```
+
+**Expected:** ✓ 100% test coverage, ✓ 100% type coverage
+
+---
+
+### 2. Project Structure
+
+```
+socket-packageurl-js/
+├── src/              # Source code
+│   ├── index.ts      # Main PackageURL class
+│   ├── parse.ts      # Parser implementation
+│   ├── builder.ts    # Builder implementation
+│   └── types.ts      # TypeScript definitions
+│
+├── test/             # Tests (mirrors src/)
+├── scripts/          # Build scripts
+└── docs/             # Documentation
+    ├── api-reference.md
+    ├── usage-examples.md
+    └── getting-started.md
+```
+
+---
+
+### 3. Essential Commands
+
+```bash
+# Development
+pnpm run dev         # Watch mode
+pnpm build           # Build for production
+
+# Testing
+pnpm test            # Run tests
+pnpm run cover       # With coverage
+
+# Quality
+pnpm run check       # Type check + lint
+pnpm run fix         # Auto-fix issues
+```
+
+---
+
+## 🧪 What is a Package URL?
+
+A Package URL (purl) standardizes software package identification:
+
+```
+pkg:npm/lodash@4.17.21
+│   │   │      │
+│   │   │      └─ Version
+│   │   └──────── Name
+│   └──────────── Namespace (optional)
+└──────────────── Type (ecosystem)
+```
+
+**Supported ecosystems:**
+- npm, pypi, cargo, gem, maven, nuget, go, docker, etc.
+
+---
+
+## 💡 Development Workflow
+
+```
+1. Branch     → git checkout -b feature/my-change
+2. Implement  → Edit src/ files
+3. Test       → pnpm test (100% coverage required)
+4. Verify     → pnpm run fix && pnpm test
+5. Commit     → Conventional commits
+6. PR         → Submit pull request
+```
+
+---
+
+## 📚 Key Concepts
+
+### 1. Spec Compliance
+
+This library implements the [Package URL specification](https://github.com/package-url/purl-spec).
+
+All changes must maintain spec compliance.
+
+### 2. Zero Dependencies
+
+Runtime has zero dependencies. All code is self-contained.
+
+### 3. Type Safety
+
+Full TypeScript support with 100% type coverage:
+
+```typescript
+import { PackageURL } from '@socketregistry/packageurl-js'
+
+const purl = new PackageURL(
+  'npm',           // type
+  null,            // namespace
+  'lodash',        // name
+  '4.17.21',       // version
+  null,            // qualifiers
+  null             // subpath
+)
+```
+
+---
+
+## 📖 Additional Resources
+
+- [API Reference](./api-reference.md) - Complete API docs
+- [Usage Examples](./usage-examples.md) - Common patterns
+- [Getting Started](./getting-started.md) - Detailed setup
+- [CLAUDE.md](../CLAUDE.md) - Development standards
+
+---
+
+## ✅ Checklist
+
+- [ ] Installed dependencies (`pnpm install`)
+- [ ] Tests passing (`pnpm test`)
+- [ ] Read [API Reference](./api-reference.md)
+- [ ] Understand Package URL spec
+- [ ] Know commit format (conventional commits)
+- [ ] Ready to contribute!
+
+**Welcome!** 🎉