meta: move code of conduct to it's own file

[MylesBorins]

Currently the code of conduct exists but it is somewhat hidden in
CONTRIBUTING.md

This PR creates CODE_OF_CONDUCT.md that contains the copy originally
found in CONTRIBUTING.md

[MylesBorins]

@jasnell@mikeal@othiym23@isaacs

[mikeal]

habitual comment about adding more ALLCAPS top-level files

Just getting that out of the way :)

But in seriousness, it should be in CONTRIBUTING.md because only CONTRIBUTING.md is linked to when submitting a pull request.

[MylesBorins]

That's reasonable... maybe we should add something to the README.md instead? My main concern is that the Code of conduct is not very discoverable

[mikeal]

A link in the README seems appropriate. While we're at it we should link to all the other files there like the COLLABORATOR_GUIDE.

[MylesBorins]

It seems like there are already a handful of links here

--> https://github.com/nodejs/node#resources-for-newcomers

I'm going to take a pass at that copy

[bnoordhuis]

But in seriousness, it should be in CONTRIBUTING.md because only CONTRIBUTING.md is linked to when submitting a pull request.

One criticism I've heard is that no one reads it because it's too big.

[silverwind]

How about putting it on either the Wiki or in doc? Not too fond of adding another root level file.

[MylesBorins]

closing in lieu of #3774