Add community guidelines

[castelao]

Thanks for the fast response. I'm sorry, but I think it would be helpful a little more information, but you don't need to make it all by yourself. There are plenty of examples that you can copy and fine-tune with small edits. Here is an (outdated) example of contributing. Your preferred publications at JOSS should have other examples.

The value of that is to save time in the future for both sides. For a contributor with low experience, you save time by don't explaining the steps every time (fork, clone, branch, edit, push, PR). On the contributor side, not everyone is fluent in software maintenance on GitHub way, so clear instructions save their time and give them more confidence to contribute. Finally, even for experienced developers, there are many ways to do it, so you make it clear how you want it, thus it is done smoothly only once.

[pnsaevik]

I appreciate your helpful suggestions. See the proposed new changes to the documentation.

[castelao]

It looks great! It's ready to merge. Thanks.