Update primercss.io website

[broccolini]

Make primercss.io a 1 page overview & archive old website

This pr is a follow-on from primer/css#315 and moves the primer.io website to this new repo, makes the website a 1 pager, and archives the old website.

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[Original pr overview]

It's been killing me for a while that we have such an out of date public website. Most primer modules have up-to-date style documentation that is a lot more useful than the out of date website, and it's probably not very obvious to people that those docs are there.

We're making good progress on the new documentation website and our intention was to make primercss.io a 1 pager of information with links to install and overview of packages, and then link to the new style guide documentation. This update sets us up for that.

In this pr

• archives old site, with link to it in case people still want to access it
• makes primercss.io a 1 page overview with summary of packages, links to all the useful things such as installation instructions, the changelog, and all the modules.
• uses latest primer-css styles

This is what it looks like:

For a more robust implementation we should automate the list of modules in each meta-package as well as version numbers. I think this static page will do for now, but we could probably make this a jekyll site and borrow some of the scripts we're using in the new documentation to keep this up-to-date.

⚠️ This pr should not be shipped until we ship the 9.3.0 release which will contain the remaining documentation and consolidated changelog.

To do

• move site to it's own repo
• check the css maps correctly to the archived site - cc @jonrohan for halp with this
• Ship primer-css 9.3.0
• Include primer-core instead of linking to build Not worth doing unless we make this a jekyll site
• update apple touch icon to new blue
• add apple touch icon
• add og meta image
• link to storybook will do when v10 is published
• make this repo publish to gh pages and turn off primer/primer-css gh page branch

cc @primer/design-systems

[broccolini]

@jonrohan I didn't see much point in installing and checking in Primer CSS as that requires adding a package.json and then mapping all the imports to the built css. I think we should do that if we turn this into a Jekyll site. I have pointed the cdn links at exact versions though in 7daa40c.