Improve the CONTRIBUTING.md.jinja2 template

[cmungall]

I like the one the energy ontology has (cc @jannahastings):

https://github.com/OpenEnergyPlatform/ontology/blob/dev/CONTRIBUTING.md

See also
https://docs.google.com/presentation/d/1nIybviEEJiRKHO2rkBMZsQ0QjtsHyU01_-9beZqD_Z4/edit#slide=id.g261c210695_0_16

https://mozillascience.github.io/working-open-workshop/contributing/

We could also eat our own dog food and improve the docs for contributing to this repo:

https://github.com/INCATools/ontology-development-kit/blob/master/CONTRIBUTING.md

[cmungall]

It would be good to take a pass at this - we really want to spread best practice as far as possible and the CONTRIBUTING.md is the best vector for this. See bio-ontology-research-group/unit-ontology#51

[matentzn]

Look at PRs, @cthoyt just started st.

I started something more crazy for SSSOM mapping-commons/sssom#175

[cmungall]

I see this PR:

• [WIP] Update contribution guidelines #598

This is a great start. But maybe we can keep it simple. We can link out to a lot of docs. We just need to tell people the basics here and avoid the mistakes that keep happening again and again such as people not making PRs on edit files (see information-artifact-ontology/IAO#256)