Add CODE_OF_CONDUCT.md in line with SciTools template

[trexfeathers]

No description provided.

[trexfeathers]

Agreed to wait for @HGWright's MANIFEST.in work, which we expect to fix the manifest CI failure. And if not, it at least creates the space for me to fix without causing conflicts 👍

[github-actions]

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[pp-mo]

From @SciTools/peloton #218 also needs doing, probably first

[scitools-ci]

• Please see: SciTools/.github#250

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[HGWright]

Finally merged.