What about remote PRs? How does this affect that?

What about checking all commits in PR and showing which ones don't have Signed-off-by?

Added a commit adding the banner for new remote PRs.

Displaying the list of "invalid" commits could end up being problematic if many commits are missing it. I think I'd rather leave this to the user.

@pingou we could add some red/green label on the commits list

But we can sort it out later if someone else will not like existing behavior. LGTM ;)

Thanks for the review!

Let's start with this and we can reconsider/adjust/improve once this is live :)