Add shellcheck action

.github/workflows/lint.yml

@@ -0,0 +1,20 @@
+name: lint
+
+on:
+  push:
+    paths:
+      - '*.sh'
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v2
+
+      - name: Lint script
+        uses: azohra/shell-linter@v0.5.0
+        with:
+          path: '*.sh'