docs: add README with features, examples, and roadmap

README.md

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+# 🏃 rnr
+
+**Clone a repo. Run tasks. No setup required.**
+
+[![Build & Test](https://github.com/CodingWithCalvin/rnr.cli/actions/workflows/build.yml/badge.svg)](https://github.com/CodingWithCalvin/rnr.cli/actions/workflows/build.yml)
+[![Integration Tests](https://github.com/CodingWithCalvin/rnr.cli/actions/workflows/integration-test.yml/badge.svg)](https://github.com/CodingWithCalvin/rnr.cli/actions/workflows/integration-test.yml)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+
+---
+
+## ✨ What is rnr?
+
+**rnr** (pronounced "runner") is a cross-platform task runner that works **instantly** on any machine. No Node.js. No Python. No global installs. Just clone and go.
+
+```bash
+git clone your-repo
+./rnr build    # It just works! 🎉
+```
+
+### 🤔 Why rnr?
+
+| Tool | Requires |
+|------|----------|
+| npm scripts | Node.js installed |
+| Makefile | Make installed (painful on Windows) |
+| Just | Just installed |
+| Task | Task installed |
+| **rnr** | **Nothing!** ✅ |
+
+rnr binaries live **inside your repo**. Contributors clone and run—zero friction.
+
+---
+
+## 🚀 Quick Start
+
+### Initialize a Project
+
+```bash
+# Download and run init (one-time setup by maintainer)
+curl -sSL https://rnr.dev/rnr -o rnr && chmod +x rnr && ./rnr init
+```
+
+This creates:
+```
+your-repo/
+├── .rnr/bin/          # Platform binaries (Linux, macOS, Windows)
+├── rnr                # Unix wrapper script
+├── rnr.cmd            # Windows wrapper script
+└── rnr.yaml           # Your task definitions
+```
+
+### Run Tasks
+
+```bash
+./rnr build        # Run the 'build' task
+./rnr test         # Run the 'test' task
+./rnr --list       # See all available tasks
+```
+
+---
+
+## 📝 Task File Format
+
+Tasks are defined in `rnr.yaml` at your project root.
+
+### Simple Commands (Shorthand)
+
+```yaml
+build: cargo build --release
+test: cargo test
+lint: npm run lint
+```
+
+### Full Task Definition
+
+```yaml
+build:
+  description: Build for production
+  dir: src/backend           # Working directory
+  env:
+    NODE_ENV: production     # Environment variables
+  cmd: npm run build
+```
+
+### Sequential Steps
+
+```yaml
+ci:
+  description: Run CI pipeline
+  steps:
+    - task: lint
+    - task: test
+    - task: build
+```
+
+### Parallel Execution
+
+```yaml
+build-all:
+  description: Build all services
+  steps:
+    - cmd: echo "Starting builds..."
+    - parallel:
+        - task: build-api
+        - task: build-web
+    - cmd: echo "✅ All done!"
+```
+
+### Nested Task Files
+
+Subdirectories can have their own `rnr.yaml`:
+
+```yaml
+# Root rnr.yaml
+api:build:
+  dir: services/api
+  task: build          # Runs 'build' from services/api/rnr.yaml
+```
+
+---
+
+## 🛠️ Built-in Commands
+
+| Command | Description |
+|---------|-------------|
+| `rnr <task>` | Run a task |
+| `rnr --list` | List available tasks |
+| `rnr --help` | Show help |
+| `rnr --version` | Show version |
+| `rnr init` | Initialize rnr in current directory |
+| `rnr upgrade` | Update rnr binaries to latest |
+
+---
+
+## 📋 Complete Example
+
+```yaml
+# rnr.yaml
+
+# Simple commands
+lint: cargo clippy
+format: cargo fmt
+
+# Full tasks
+build:
+  description: Build release binary
+  env:
+    RUST_LOG: info
+  cmd: cargo build --release
+
+test:
+  description: Run all tests
+  cmd: cargo test --all
+
+# Multi-step workflow
+ci:
+  description: Full CI pipeline
+  steps:
+    - task: format
+    - task: lint
+    - task: test
+    - task: build
+
+# Parallel builds for monorepo
+build-all:
+  description: Build all services
+  steps:
+    - parallel:
+        - dir: services/api
+          cmd: cargo build --release
+        - dir: services/web
+          cmd: npm run build
+    - cmd: echo "🎉 Build complete!"
+
+# Deploy workflow
+deploy:
+  description: Deploy to production
+  steps:
+    - task: ci
+    - cmd: ./scripts/deploy.sh
+```
+
+---
+
+## 🌍 Platform Support
+
+| Platform | Architecture | Status |
+|----------|--------------|--------|
+| Linux | x86_64 | ✅ |
+| macOS | x86_64 | ✅ |
+| macOS | ARM64 (Apple Silicon) | ✅ |
+| Windows | x86_64 | ✅ |
+
+---
+
+## 🔮 Roadmap
+
+- [ ] Task dependencies (`depends: [build, test]`)
+- [ ] Conditional execution (`if: ${{ env.CI }}`)
+- [ ] Watch mode (`watch: [src/**/*.rs]`)
+- [ ] Variable interpolation (`${{ vars.version }}`)
+- [ ] Caching / incremental builds
+- [ ] Interactive task picker
+
+See [DESIGN.md](DESIGN.md) for the full roadmap.
+
+---
+
+## 🤝 Contributing
+
+Contributions are welcome! Please read our contributing guidelines and submit PRs.
+
+### Development
+
+```bash
+# Clone the repo
+git clone https://github.com/CodingWithCalvin/rnr.cli
+cd rnr.cli
+
+# Build
+cargo build
+
+# Run tests
+cargo test
+
+# Run locally
+cargo run -- --help
+```
+
+---
+
+## 👥 Contributors
+
+<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
+<!-- prettier-ignore-start -->
+<!-- markdownlint-disable -->
+
+<!-- markdownlint-restore -->
+<!-- prettier-ignore-end -->
+<!-- ALL-CONTRIBUTORS-LIST:END -->
+
+---
+
+## 📄 License
+
+MIT License - see [LICENSE](LICENSE) for details.
+
+---
+
+<p align="center">
+  Made with ❤️ by <a href="https://github.com/CodingWithCalvin">CodingWithCalvin</a>
+</p>