Reshuffle the Guides docs landing page to match the section contents

[ericronne]

This issue is part of Epic 3B: Fixes from legacy issue queue.

"Install" is noted twice on the Guides index page, and neither summary is a good intro to the section to which it links. Remedy.

[jessicaschilling]

This is a little more complex than it looks at first, because it involves Hugo's auto-generated landing pages - just FYI.

[jessicaschilling]

See below for screenshot of a compromise solution -- since we're leaving Hugo behind with deployment of the docs beta, it didn't seem a good use of time to dig into its means of auto-generating content on page bundle index pages.

What this does:

• Removes duplicate content
• Fixes typos and poor wording in original top-of-page text about install page
• Adds a prominent visual callout (in existing design language) at the top of the page leading to the install guide

What this doesn't do:

• Hide the poorly-formatted, auto-generated Hugo content at the bottom of the page for "install IPFS" or "addressing in browsers"

@ericronne, I'm taking the liberty of closing this issue, but please reach out if you want to iterate on it more! Thanks.