Enable "require sign-off on web-based commits" in repository settings

[bluikko]

If the repository policy is that commits must have sign-offs, then it would be helpful to enable the setting Require contributors to sign off on web-based commits in repository settings.

Then when someone, likely a new contributor who does not know about the requirement, does a simple PR using the GitHub web interface - say, a trivial docs update - then there will be a tickbox "enable sign-off" when doing the commit.

[rhatdan]

Done

[lsm5]

Done

guess we can close this then. @bluikko please reopen if you still see the issue. Thanks