Switch docs to mamba and Mambaforge

[xylar]

Addresses #427

[forsyth2]

@xylar Thanks for putting this together. I'm following along with the instructions but at this command I get bash: mamba: command not found.

[xylar]

Did you install Mambaforge? If not, did you got to the Troubleshooting section below?

[xylar]

@forsyth2, if my troubleshooting section isn't intuitive, feel free to reorganize (either by suggesting changes or pushing to my branch). You could move that stuff back as (hopefully) redundant parts of the basic installation.

[xylar]

I've gone ahead and reorganized in a way that I hope is more intuitive for you.

[forsyth2]

Thanks @xylar. Following these instructions, I was able to set up both the production environment and the development environment. I still need to make the changes mentioned in #397 however.

[xylar]

@forsyth2, I see, I had forgotten how the issues were interrelated. You are right that the yaml file should also be updated to switch sphinx-multiversion to come from conda-forge, not pip. That seems like a trivial change.

I think everything else in #397 relates to GitHub Actions (which is installing a lot of stuff from pip). I didn't see anywhere else that pip was being used in zppy (besides pip install ., which is fine). So I think other than maybe the one sphinx-multiversion change, #397 is not related to this change, which is about how developers interact with zppy, rather than what CI does.

[forsyth2]

@xylar Is this ready to merge?

[xylar]

@forsyth2, yes, as far as I'm concerned, this is ready to merge.