update contributing guides

[jukent]

Updates project-wide contribution (changed name to reduce a frequent confusion I have), updates repo specific contribution guide, updates Cookbook guide to match MyST workflow and for clarity, and adds a lightweight Cookbook guide.

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[r-ford]

Related: #428, #431, #447, #518, #534

[jukent]

Related: #428, #431, #447, #518, #534

Thanks for reminding me of these issues @r-ford I'm off for the day but will look at making everything consistent tomorrow.

[brian-rose]

I have some reservations about renaming several of these files because that will likely break existing links. Since we're not running full link checking right now, we may not spot all broken internal links, and may also inadvertently break external links to our content. So I think there needs to be a cost-benefit consideration.

[jukent]

Heard @brian-rose I changed the file name back.

I updated the language and a few other things.

Any insight why it looks like I'm adding a myst.yml file? I don't remember us removing one or why we wouldn't have needed it.

[erogluorhan]

Looks good to me; thanks for this!

[erogluorhan]

Any insight why it looks like I'm adding a myst.yml file? I don't remember us removing one or why we wouldn't have needed it.

Actually, from the history, myst.yml seems to have been moved into /portal with PR#519.

With this PR got merged, we have a duplicate file now in the root as well.

[brian-rose]

#519 was necessary to restore the correct URLs for pages on the portal site. Also keeping myst.yml inside the /portal directory and running the myst build from there keeps the build process consistent with our previous portal, which means fewer edits to contributors guides etc.