ci: add lint for C and shell format

.github/workflows/lint.yml

@@ -0,0 +1,39 @@
+name: Lint
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  lint-c:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: install tools
+        run: sudo apt-get install indent
+
+      - name: indent
+        run: make indent
+
+      - name: check formatting
+        run: git diff --exit-code
+
+  lint-shell:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Run the sh-checker
+        uses: luizm/action-sh-checker@v0.1.12
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          SHELLCHECK_OPTS: -e SC1004 # exclude some shellcheck warnings.
+          SHFMT_OPTS: -s # arguments to shfmt.
+        with:
+          sh_checker_shellcheck_disable: true
+          sh_checker_comment: true