[WIP] Added instructions for CmdStan tarball builder

[bbbales2]

Adding instructions to use the CmdStan tarball builder Github action (https://github.com/stan-dev/cmdstan/actions/workflows/tarball.yml)

Here is a build of the initial instructions: cmdstan-tarball-builder.html.zip (Edit: updated)

[bbbales2]

@dashadower @hyunjimoon give this a go and tell me if these instructions are clear or not.

I'm not super happy with the formatting on the font size/formatting on the screenshots. If you can think of a better way of presenting the information, lemme know. As plain text I think it's sometimes frustrating to figure out exactly where to click.

[Dashadower]

Thanks! It looks perfectly fine for me, at least on mobile.

[hyunjimoon]

Yes, I have asked rok and have built the current FASO version here. Nice feature.

[bbbales2]

@rok-cesnovar I didn't know quite where this document should live so I've just left it as an open pull so I can send people here (the html in the zip file at the top is up to date). I made it a case study cause then I could have images, but I don't think I want to put it on the case studies page like a feature we're gonna support long term or anything.

Next time I look at the new Math contributor docs I'll move it in there. In the interim, let's just leave this pull open.

[rok-cesnovar]

Cool, on board with that.