Require DCO sign-off for new commits

[GeorgLink]

This issue is to activate protobot/dco (or similar bot) to check that all commits have a sign-off in this repository.

The CHAOSS Project Charter section 8.2.1 requires that all contributions are signed-off. The CHAOSS project has been piloting the use of DCO sign-offs. Once contributors know how to do it, sign-offs are easy to do with little overhead.

For users of the git command line interface, a sign-off is accomplished with the -s as part of the commit command: git commit -s -m 'This is a commit message'

For users of the GitHub interface, a sign-off is accomplished by writing Signed-off-by: Your Name <YourName@example.org> into the commit comment field. This can be automated by using a browser plugin like scottrigby/dco-gh-ui

To-Do for repo maintainers: Please inform your contributors about DCO sign-offs and comment on this issue when your are ready for the DCO bot to be activated on this repository.

[valeriocos]

done @GeorgLink

[GeorgLink]

Thanks @valeriocos