Add a badge for the Nix workflow to the README #17

	name: Rust
	on: [push, pull_request]
	jobs:
	test:
	name: Test on Rust ${{ matrix.rust_version }}
	runs-on: ubuntu-latest
	strategy:
	matrix:
	rust_version: [stable, beta, nightly]
	steps:
	- uses: actions/checkout@master
	- name: Set Rust version
	run: rustup default ${{ matrix.rust_version }}
	- name: Install Clippy and Rustfmt
	run: \|
	rustup component add clippy
	rustup component add rustfmt
	- name: Format
	run: cargo fmt -- --check
	- name: Lint
	run: cargo clippy
	- name: Build
	run: cargo build --verbose
	- name: Run tests
	run: cargo test --verbose
	- name: Actually run the thing!
	run: ls -l \| cargo run -- --title "Little boxes on the hillside"

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