chore: add comment on PRs with unsigned commits (#768)

.github/workflows/check-pr.yml

@@ -44,6 +44,23 @@ jobs:
           header: pr-title-lint-error
           delete: true
 
+  check-signed:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      # Check commit signature and add comment if needed
+      - name: Check signed commits in PR
+        uses: 1Password/check-signed-commits-action@v1
+        with:
+          comment: |
+            Thank you for opening this pull request!
+
+            We require commits to be signed and it looks like this PR contains unsigned commits.
+
+            Get help in the [CONTRIBUTING.md](https://github.com/ratatui-org/ratatui/blob/main/CONTRIBUTING.md#sign-your-commits)
+            or on [Github doc](https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits).
+
   check-breaking-change-label:
     runs-on: ubuntu-latest
     env: