Add .github folder

.github/workflows/shellcheck.yml

@@ -0,0 +1,32 @@
+name: Shellcheck
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+  schedule:
+    - cron: "5 1 * * *"
+
+jobs:
+  shellcheck:
+    name: Shellcheck
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Get changed files
+      id: changes
+      run: |
+        if ${{ github.event_name == 'pull_request' }}; then
+          echo "files=$(git diff --name-only -r HEAD^1 HEAD | xargs)" >> $GITHUB_OUTPUT
+        else
+          echo "files=$(git diff --name-only ${{ github.event.before }} ${{ github.event.after }} | xargs)" >> $GITHUB_OUTPUT
+        fi
+
+    - name: Run ShellCheck
+      if: steps.changes.outputs.files != ''
+      run: |
+        echo "${{ steps.changes.outputs.files }}" | xargs shellcheck