Request for git merge --signoff

[Dan Kohn <dan@linuxfoundation.org>]

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