Adopt the OCaml Code of Conduct

[rikusilvola]

The OCaml Code of Conduct can be found in ocaml/code-of-conduct and has been discussed in this Discourse thread.

We propose adopting it for tarides/dune-release as well.

Once adopted, the list at ocaml/code-of-conduct needs to be updated.

• [x] #474
• [x] Update List of Adopters https://github.com/ocaml/code-of-conduct/pull/10

[Leonidas-from-XIV]

Done, thanks!