docs(conduct): add a "code of conduct" for democracy-ia

[gregswindle]

User story summary

As a community member,
I need a Code of Conduct
In order to manage and enforce civil behavior.

Acceptance criteria

TBD.

Notes

1. GitHub themselves recommend maintainers select from one of two Codes of Conduct:
   • Contributor Covenant Code of Conduct
   • Citizen Code of Conduct
2. We can always modify them within the terms of their Creative Commons licenses.