ci: add vale docs linter

.github/workflows/ci.yml

@@ -42,3 +42,11 @@ jobs:
         echo "::add-matcher::.github/actionlint-matcher.json"
         bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
         ./actionlint
+
+  reviewdog:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: errata-ai/vale-action@reviewdog
+      with:
+        fail_on_error: true

.vale.ini

@@ -0,0 +1,5 @@
+StylesPath = .github/styles
+MinAlertLevel = suggestion
+
+[*.md]
+BasedOnStyles = Vale