Add rustfmt action

Author: sfackler

.github/workflows/ci.yml

@@ -0,0 +1,18 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - master
+  push:
+    branches:
+      - master
+
+jobs:
+  rustfmt:
+    name: rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: sfackler/actions/rustup@master
+      - uses: sfackler/actions/rustfmt@master