Add cargo audit check

.github/workflows/cargo-audit.yml

@@ -0,0 +1,16 @@
+name: Audit Rust dependencies
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '30 3 * * *' # At 3:30 every day
+
+jobs:
+  audit:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/audit-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}