Create CODE_OF_CONDUCT.md

[mekarpeles]

Closes #2319
Closes #2441

[hornc]

Hi @tapaswenipathak , we have a PR for a code of conduct! Please review and let us know if this looks fine, or whether there is anything missing. It should be all the standard and required content from the https://www.contributor-covenant.org/ guidelines which we a taking up. Thanks!

[tfmorris]

For those who are curious, here's the diff against the file in PR #2441:

$ diff CODE_OF_CONDUCT*
58c58
< reported by contacting the project team at openlibrary@archive.org. All
---
> reported by contacting the project team at openlibrary-maintainers@archive.org

[cdrini]

For anyone following, openlibrary-maintainers@archive.org will send a message to the 3 ol staff (Charles, Mek, and I), with Mek being in charge for handling it. We were not 100% sure about having it go to all three of us, but since we're such a small team (and can't have an impartial person look into it) we thought having it go to all three would be a good "checks and balances". Having one person responsible for responding was a way to avoid bystander effect.