Do something like [this example from Fd.io|
https://git.fd.io/trex/tree/signedoff] for the three codebases we're importing:

Git-foo is something like:

> git log --format=format:"%h %an %ae " ca1d6e1fe1c0ab430a56a7fccddbc08fe7d3b6d5..4f72440f1919d031e49d4f894631c6ab5b4aa490 --author='^(?!Daniel Farrell).*$' --perl-regexp

I have sign-off commits pushed for every contributor on the dco Gerrit topic, but I think I need to update them to include the shortlog of the commit as the hash may get rewritten.

Imported from Trello