introduce reviewdog/action-shellcheck

.github/workflows/reviewdog.yml

@@ -0,0 +1,16 @@
+name: reviewdog
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+jobs:
+  shellcheck:
+    name: runner / shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: reviewdog/action-shellcheck@v1
+        with:
+          github_token: ${{ secrets.github_token }}
+          reporter: github-check