Add CI for checking markdown format.

.github/workflows/ci.yml

@@ -85,6 +85,15 @@ jobs:
       - name: Run tests (with prefix_symbols)
         run: cargo test --features prefix_symbols --verbose
 
+  markdown_lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: DavidAnson/markdownlint-cli2-action@v18
+        with:
+          config: '.markdownlint.yaml'
+          globs: '**/README.md'
+
   # NOTE: In GitHub repository settings, the "Require status checks to pass
   # before merging" branch protection rule ensures that commits are only merged
   # from branches where specific status checks have passed. These checks are
@@ -93,7 +102,7 @@ jobs:
   ci:
     name: CI status checks
     runs-on: ubuntu-latest
-    needs: build
+    needs: [build, markdown_lint]
     if: always()
     steps:
       - name: Check whether all jobs pass

.markdownlint.yaml

@@ -0,0 +1,6 @@
+{
+  "MD013": false, # Line length limitation
+  "MD033": false, # Enable Inline HTML
+  "MD041": false, # Allow first line heading
+  "MD045": false, # Allow Images have no alternate text
+}