Add linters (#1)

* Add linters and ignore antigen.zsh

.github/workflows/linters.yml

@@ -0,0 +1,43 @@
+name: reviewdog
+on: [ push ]
+jobs:
+  linters:
+    name: Linters
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: GitHub Actions
+        uses: reviewdog/action-actionlint@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          reporter: github-pr-review
+
+      - name: detect-secrets
+        uses: reviewdog/action-detect-secrets@master
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          reporter: github-pr-review
+
+      - name: markdownlint
+        uses: reviewdog/action-markdownlint@v0
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          reporter: github-pr-review
+
+      - name: shfmt
+        uses: reviewdog/action-shfmt@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          shfmt_flags: |
+            --find
+            --list
+            --write
+            --diff
+            --simplify
+            --language-dialect bash
+            --indent 2
+            --binary-next-line
+            --case-indent
+            --space-redirects
+            --func-next-line