Port GenericSetup docs

[stevepiercy]

GenericSetup docs have not been ported to Plone 6 yet. I can convert this file https://github.com/plone/documentation/blob/5.2/develop/addons/components/genericsetup.rst from .rst to .md, then you can fiddle with it. Where should its content go? I think most of it is how-to guide.

Originally posted by @stevepiercy in #1748 (comment)

[stevepiercy]

lol, I already converted that file to MyST on Jul 12, 2022.

https://github.com/plone/documentation/blob/5.2-myst/5.2-myst/develop/addons/components/genericsetup.md