Update README.md

Signed-off-by: Severin Kaderli <severin@kaderli.dev>

README.md

@@ -10,3 +10,29 @@ Add the configuration in the `package.json` file:
   "prettier": "@severinkaderli/prettier-config"
 }
 ```
+
+# CI
+The formatting can be checked using the following job in GitHub-compatible workflows.
+
+```yaml
+check-format:
+    name: Check formatting
+    runs-on: ubuntu-latest
+    steps:
+        -   name: Checkout the repository
+            uses: actions/checkout@v4
+
+        -   name: Install Node.js
+            uses: actions/setup-node@v3
+            with:
+                node-version: 20
+
+        -   name: Add custom npm package registry
+            run: npm config set @severinkaderli:registry https://git.kaderli.dev/api/packages/severinkaderli/npm/
+
+        -   name: Install dependencies
+            run: npm ci
+
+        -   name: Check formatting
+            run: npm run format:check
+```