Contributer License Agreement / Developer Certificate of Origin

We need some way to ensure that contributions are valid under our license. There are two ways to achieve this. The first option is some kind of CLA. CLAs are not very liked by developers and gitlab does not seem to provide any explicit support. The second is by using a Developer Certificate of Origin (DCO), which gitlab itself also uses. This would only require us to create a DCO document in our project and add a requirement that users sign their commits.

1. Sign your work. Your signature certifies your submission according to the
   articles of the [Developer Certificate of Origin](https://gitlab.ewi.tudelft.nl/eip/labrador/queue/blob/master/DCO).
   The sign-off should be in the form:

    ````
    Signed-off-by: John Doe <john.doe@example.com>
    ````

    You must use your real name and email, pseudonyms or anonymous contributions
    are not allowed. If you set your user.name and user.email git configs, you can
    sign your commit automatically with git commit -s.

DCO document:

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
1 Letterman Drive
Suite D4700
San Francisco, CA, 94129

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.