Implement action.

README.md

@@ -1 +1,19 @@
 # Setup Rust
+
+A GitHub action for setting up Rust and Cargo. Will automatically install the appropriate toolchain
+with `rustup` by inspecting the `RUSTUP_TOOLCHAIN` environment variable or the `rust-toolchain.toml`
+configuration file.
+
+## Installation
+
+```yaml
+# ...
+jobs:
+  ci:
+    name: CI
+    runs-on: ubuntu-latest
+    steps:
+      # ...
+      - uses: moonrepo/setup-rust@v0
+      - run: cargo test
+```