Endorse a finite number of package managers and document how to use them for contributing, including limitations

[mfisher87]

We have a conda dev environment specification, but we don't really document how to use it. For a pure python project, I expect pip install --editable .[dev,...], but we've set up our project for poetry development environment, and our contributing doc doesn't say how to use it. What package managers do we want to endorse / encourage and document for our contributors?

Limitations: For example, our environment-dev.yml isn't perfectly up to date. Let's document that or change the file so that it doesn't need to be kept up to date, as suggested by @jhkennedy here

Extracted from #449