Add CI workflow

Author: jishengyang-cal

.github/workflows/ci.yml

@@ -0,0 +1,18 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - name: Format
+        run: cargo fmt --check
+      - name: Test
+        run: cargo test
+      - name: CLI contract
+        run: make check

README.md

@@ -1,5 +1,7 @@
 # GATL AD Lab
 
+Status: external numeric check harness for `gatl-core` `risk-models` artifacts.
+
 GATL AD Lab is an external numeric check harness for `gatl-core` risk-model
 artifacts. It consumes `gatl risk-models` JSON, evaluates the typed scalar RPN
 expression, executes the exported reverse derivative instruction skeleton, and