Add a simple contributing guide

Author: MMK21Hub

CONTRIBUTING.md

@@ -0,0 +1,18 @@
+# Contributing guide
+
+PRs are welcome!
+
+This guide is quite barebones - if you have any questions, feel free to open an issue or contact [@MMK21](https://github.com/MMK21Hub/).
+
+## Setup
+
+We use Rust and Cargo, as is standard for most Rust projects.
+
+## Publishing a new release
+
+1. Bump version
+   - Ensure Cargo.toml and Cargo.lock are commited
+2. Run `build_binaries.sh`
+   - See the script for usage details
+3. Create a GitHub release
+   - Auto-generate release notes from PR titles & add some blurb