Add README.md (#27)

Author: tychedelia

README.md

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 # libprocessing
+
+libprocessing is an experimental native library with the goal of supporting the implementation of the core Processing API in a variety of languages. The library is written in the [Rust programming language](https://rust-lang.org/) and built on top of the [Bevy game engine](https://bevy.org/). libprocessing uses [WebGPU](https://webgpu.org/) as its rendering backend and is designed to (eventually) support desktop, mobile, and web targets.
+
+## Getting started
+
+### Rust
+
+You'll need to install the Rust toolchain to work on this project. Most users will want to install Rust via [`rustup`](https://rustup.rs/), which helps manage Rust toolchain versions.
+
+## Contributing
+
+We want your help building this library! You can see a list of outstanding tasks in our [issues](https://github.com/processing/libprocessing). However, while we're still in the early phases, consider checking in with us first in the `#devs-chat` channel on [Discord](https://discord.gg/h99u95nU7q) to coordinate our efforts.
+
+You can read our project design principles [here](./docs/principles.md).