Provide a `CONTRIBUTING` file

[Niols]

WIP; please don't review at this point.

[Niols]

I find it hard to start a review process on such a file. For now, I have been hacking something based on Mozilla Science Lab's guidelines to write a CONTRIBUTING file that in particular refers to Atom's CONTRIBUTING.md. In a first round of reviews, I would like to ask the following questions to a reviewer:

1. Is this the kind of content you expected from a CONTRIBUTING.md file?
2. Does the scope seem right to you?
3. Are there important things that are missing?
4. Are there things currently in the file that shouldn't be there? (If yes: should they just disappear or go to another file?)

Gabriel mentioned the idea of having a look at Nickel's HACKING.md file and I will be doing that now.

[facundominguez]

Here's how GHC does it: https://gitlab.haskell.org/ghc/ghc/-/blob/master/HACKING.md

For cooked, I'd keep it lean in the beginning.

• Welcome issues and pull requests.
• Explain that issues are a good way to reach maintainers with questions.
• Explain how to build and test patches ahead of submitting PRs.
• Maybe examples in cooked-smart-contracts need to be tested as well (?).

Then it would make sense to add other things as the need arises.

The Atom guide is too big of an example, I'd say.

[facundominguez]

I found today the contributing file from plutus-apps: https://github.com/input-output-hk/plutus-apps/blob/main/CONTRIBUTING.adoc

I share it not to imitate, but because it may surface details that people here consider relevant.