Set up Copilot instructions

.github/copilot-instructions.md

@@ -0,0 +1,59 @@
+# Copilot Instructions
+
+This repository contains **Natura**, a Rust spring animation library for smooth, natural motion in 2D and 3D contexts.
+
+## Project Overview
+
+- **natura**: Core library implementing damped harmonic oscillator (spring) physics
+- **bevy-natura**: Plugin for integration with the Bevy game engine
+- **examples/**: Example applications using coffee, Bevy, and standalone Rust
+
+## Build Commands
+
+```bash
+# Build entire workspace
+cargo build
+
+# Build only the core library
+cargo build -p natura
+
+# Build specific example
+cargo run -p simple
+cargo run -p coffee-2d
+cargo run -p bevy-simple
+```
+
+## Test Commands
+
+```bash
+# Run all tests
+cargo test
+
+# Run tests for core library only
+cargo test -p natura
+```
+
+## Code Style and Conventions
+
+- Follow standard Rust idioms and the [Rust API Guidelines](https://rust-lang.github.io/api-guidelines/)
+- Use `rustfmt` for code formatting
+- Add documentation comments (`///`) for public APIs
+- Include doc tests in documentation when illustrating API usage
+- Use descriptive variable names that reflect physics terminology (e.g., `angular_frequency`, `damping_ratio`, `equilibrium_pos`)
+
+## Architecture
+
+The core spring animation is based on Ryan Juckett's damped simple harmonic oscillator algorithm. Key types:
+
+- `Spring`: Main struct for computing spring animation coefficients
+- `DeltaTime`, `AngularFrequency`, `DampingRatio`: Newtype wrappers for type safety
+- `Projectile`: Simulator for projectile/particle motion
+- `Point`, `Vector`: Basic geometry types
+
+## Making Changes
+
+- Keep changes minimal and focused
+- Maintain backward compatibility for public APIs
+- Add tests for new functionality
+- Update documentation when modifying public APIs
+- Consider both 2D and 3D use cases when making changes to the core library