Request for git merge --signoff

https://github.com/coreinfrastructure/best-practices-badge is a user of the https://github.com/probot/dco bot which checks that commits have a signoff. The issue is that there is no `--signoff` option in git for merge commits, which is a standard part of our workflow with feature branches. Here is a workflow where we currently get stuck:

```sh (master)$ git checkout -b feature-branch # make some changes (feature-branch)$ git commit -sam 'Adding features' # Changes have occurred on master so need to add them for easier merge (feature-branch)$ git fetch (feature-branch)$ git merge origin/master # Save default commit message (feature-branch)$ git push # This now fails the DCObot check because the merge commit is not signed. ```

This alternative workflow works, but is obviously tedious:

```sh # First 3 steps are the same (feature-branch)$ git merge origin/master # Save default commit message (feature-branch)$ git commit --amend -s # Commit message now has signoff line (feature-branch)$ git push # This now passes the DCObot check. ```

Or, I could manually add the Signoff line to the proposed git merge commit message, which would allow me to skip the `--amend` step.

Could you please add a `--signoff` option to `git merge`?

Probot issue reference: https://github.com/probot/dco/issues/13 -- Dan Kohn <mailto:dan@linuxfoundation.org> Executive Director, Cloud Native Computing Foundation <https://cncf.io/> tel:+1-415-233-1000