ci: Create DCO.md to help contributors (#3171)

Signed-off-by: Meenakshi Sharma <163925564+nvda-mesharma@users.noreply.github.com>
Co-authored-by: Ryan McCormick <rmccormick@nvidia.com>

.github/workflows/dco_comment.yml

+name: DCO Commenter
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  issues: write
+  checks: read
+
+jobs:
+  dco-comment:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Get DCO status
+        id: dco
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const { data: checks } = await github.rest.checks.listForRef({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              ref: context.payload.pull_request.head.sha,
+            });
+
+            const dco = checks.check_runs.find(run => run.name === "DCO");
+            core.setOutput("conclusion", dco ? dco.conclusion : "not_found");
+
+      - name: Comment if DCO failed (deduped)
+        if: steps.dco.outputs.conclusion == 'failure'
+        uses: peter-evans/create-or-update-comment@v4
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          issue-number: ${{ github.event.pull_request.number }}
+          body: |
+            ⚠️ Your pull request failed the DCO check.
+            Don’t worry! Check out our [DCO Troubleshooting Guide](https://github.com/ai-dynamo/dynamo/blob/main/DCO.md) for step-by-step instructions to fix it quickly.
+          edit-mode: replace

CONTRIBUTING.md

@@ -191,3 +191,6 @@ You may type this line on your own when writing your commit messages.
 However, if your user.name and user.email are set in your git configs,
 you can use `-s` or `--signoff` to add the `Signed-off-by` line to
 the end of the commit message.
+
+⚠️ **Contributor-Friendly DCO Guide:**
+If your pull request fails the DCO check, don’t worry! Check out our [DCO Troubleshooting Guide](DCO.md) for step-by-step instructions to fix it quickly.

DCO.md

+# ✅ Fixing DCO Check Failures
+
+The **Developer Certificate of Origin (DCO)** check ensures all commits are signed off.
+ If your PR fails the DCO check, here’s how to fix it.
+
+---
+
+## 🖥️ Option 1: Fix via GitHub Web Editor
+ ⚠️ Works only if your PR has 1 commit.
+
+1. Go to your **Pull Request** → **Commits** tab.
+2. Click the **⋯ menu** → **Edit commit message**.
+3. Add this line at the end of the commit message:
+
+   ```text
+   Signed-off-by: Your Name <your.email@example.com>
+   ```
+4. Save changes → GitHub will create a new commit with sign-off.
+5. Re-run the DCO check.
+
+## 📦 Option 2: Fix via GitHub Desktop
+
+1. Open your branch in GitHub Desktop.
+2. Go to Repository → Repository Settings → Commit Behavior.
+3. Check ✅ Always sign-off commits.
+4. Amend the last commit:
+      - Right-click the commit → Amend Commit.
+      - Save again with sign-off enabled.
+5. Push with force (if required):
+    ```
+    git push --force-with-lease
+    ```
+
+## 💻 Option 3: Fix via CLI (Multiple Commits)
+
+1. Enable sign-off in your config:
+   ```
+    git config --global user.name "Your Name"
+    git config --global user.email "your.email@example.com"
+   ```
+2. Re-sign commits interactively:
+   ```
+    git rebase -i HEAD~N
+   ```
+   Replace N with the number of commits to fix.
+   Mark commits as edit, then run:
+   ```
+    git commit --amend --signoff
+    git rebase --continue
+   ```
+3. Push with:
+   ```
+    git push --force-with-lease
+   ```
+
+## 🔀 If Your Branch Is Messy After Syncing with main
+
+- Simplest fix: squash all commits into a single new signed commit (via Desktop or CLI).
+- Alternatively, ask a maintainer to Squash and Merge with a sign-off on merge.
+
+## ✨ Pro Tips
+This ensures you’ll never fail DCO again.
+
+- Use the -s flag when committing from CLI:
+   ```
+     git commit -s -m "Your commit message"
+   ```
+- Turn on Always sign-off commits in your client (GitHub Desktop or Git CLI).
+    1. GitHub Desktop
+       Turn on Always sign-off commits in your client.
+
+    2. Git CLI
+       You can always sign-off commits automatically using a commit template (NOTE: This will only work if you use enter your commit message interactively with `git commit`, and will _not_ work with `git commit -m "<message>"`):
+       1. Create ~/.git-commit-template.txt with:
+        ```
+          Signed-off-by: Your Name <your.email@example.com>
+         ```
+    2. Tell Git to use it:
+       ```
+        git config --global commit.template ~/.git-commit-template.txt
+       ```