Use `description` front-matter as _lead_ text on page.

[johnnymatthews]

Across the docs we have stuff like this in content:

+++
title = "Quicknode setup"
description = "A walkthrough for operators who want to run a Shinzo Generator client but would rather pay a managed node provider than run and babysit their own Ethereum execution node."
+++

Most of the time, the description variable serves are a good, short introduction as to what $this page is about. It could be useful to use description as lead-text for pages. This lead-text would be smaller than the main page title, but larger than the rest of the main content to show that it's more important/draw the readers eye.

Tasks

• Edit the content template to use description at the start of each page.
  • If no description field is present, don't display any lead-text.
• Style the .lead-text class (or whatever we went up calling it) to look distinct from the rest of the copy on the page.