Improve documentation website

[nmn]

Made the following improvements:

1. Added a new section to the home page with a quick overview of the top stylex features
2. Created an "Introduction" page and moved appropriate content from other pages to it
3. Improved "Installation" page
4. "Get Started" link on Home page now goes to the "Installation" page
5. Replaced "Learn" CTA with an "API Reference" CTA.

Preview Link: https://stylex-docusaurus-11zzqvnrr-nmn.vercel.app

[github-actions]

compressed-size: runtime library

Size change: 0.00 kB
Total size: 2.36 kB

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Filename: gzip (minify)	kB size	kB change	% change
./packages/stylex/lib/stylex.js	1.02 (3.53)	0.00 (0.00)	0.0% (0.0%)
./packages/stylex/lib/StyleXSheet.js	1.34 (3.41)	0.00 (0.00)	0.0% (0.0%)

[github-actions]

compressed-size: e2e bundles

Size change: 0.00 kB
Total size: 1119.39 kB

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Filename: gzip (minify)	kB size	kB change	% change
./apps/rollup-example/.build/bundle.js	1005.22 (9872.52)	0.00 (0.00)	0.0% (0.0%)
./apps/rollup-example/.build/stylex.css	114.18 (455.95)	0.00 (0.00)	0.0% (0.0%)

[necolas]

More changes to "Thinking in StyleX"

1. Update "And the stylex() or stylex.props() calls are executed at runtime." to remove mention of stylex()

2. Update "StyleX disallows this entire class of selectors. This currently makes some patterns in CSS impossible: e.g. It is currently impossible for a child element to have conditional styles when it's parent is hovered. Our goal is to support these patterns without sacrificing style encapsulation." It's technically possible using CSS vars as tokens. We should keep "Our goal is to support ...without sacrificing style encapsulation. For example, child elements cna be conditionally styled when a parent is hovered by..."

3. Recommend removing this entirely: "Tailwind CSS is popular and lets you author your styles by putting extremely terse utility class names directly on your markup. This is great for authoring styles quickly, but in our opinion, in the long run, it makes the styles harder to read and maintain. It can also have a steeper learning curve up-front."

[nmn]

New URL: https://stylex-docusaurus-moxa15he6-nmn.vercel.app

[necolas]

Shouldn't this be removed since below we describe how child elements can have conditional styles when parents are hovered - using variables

[nmn]

I'm going to make this simpler and more vague.

[necolas]

A couple more minor issues. I think the <details> rendering that you're using to collapse bundler examples doesn't look great right now. And the options shown for each of the bundlers are different.

Also noticed a few "bad patterns" in the CSS for the docs themselves, which brings up the question of what is still supported in the OSS release.

[necolas]

Approving to unblock as it's basically there!

[nmn]

Latest link: https://stylex-docusaurus-jpo0wgtgl-nmn.vercel.app