Create initial CI

I've chosen not to deny warnings in CI because we currently have warnings.

Once #1 lands, we can enforce cleanliness of warnings

.github/workflows/rust.yml

@@ -0,0 +1,20 @@
+name: Rust
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+    - uses: dtolnay/rust-toolchain@stable
+    - name: Check
+      run: cargo check