docs: Add -s to sign off empty commits that retriggers CI (argoproj#7628

)

Signed-off-by: Yuan Tang <[email protected]>

docs/developer-guide/ci.md

@@ -15,7 +15,7 @@ Since the CI pipeline is triggered on Git commits, there is currently no (known)
 If you are absolutely sure that the failure was due to a failure in the pipeline, and not an error within the changes you committed, you can push an empty commit to your branch, thus retriggering the pipeline without any code changes. To do so, issue
 
 ```bash
-git commit --allow-empty -m "Retrigger CI pipeline"
+git commit -s --allow-empty -m "Retrigger CI pipeline"
 git push origin <yourbranch>
 ```