feat(docs): add markdown linter for exercises README.md files

.github/workflows/lint.yml

@@ -0,0 +1,18 @@
+name: Lint
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: DavidAnson/markdownlint-cli2-action@v9
+        with:
+          globs: "exercises/**/*.md"