Add Code of Conduct link directly into footer

[ayhanxian]

As discussed with @lwasser (in relation to issue #396 of the pyopensci.github.io repo), I'm creating this issue to track the progress of adding a CoC URL directly in the footer for https://www.pyopensci.org/

[kierisi]

@all-contributors please add @ayhanxian for code, review

[allcontributors]

@kierisi

I've put up a pull request to add @ayhanxian! 🎉