DCO review

[dhh1128]

The existing peer DID spec was built mostly with DCO enforced against its repo. At one point I went back and looked at commits and came to the conclusion that it had IP integrity. We also did a quick review of listed contributors, making sure that all of them were DIF members covered under DIF's contributor agreements. All of the big conceptual contributions come from DIF members for sure. See the issue history on openssi/peer-did-method-spec#82. However, it would be good to raise our level of confidence in this spec by doing 2 additional due diligence tasks:

1. Make sure DCO is now enabled for this repo.
2. Run a formal DCO check against the entire repo history to make sure we didn't miss anything in our informal checks.