Mention hints across the getting-started docs and the landing page

Basic Usage gains a live hints demo with its code, replacing a dangling
paragraph that promised a single-step tour example which never followed.
Installation covers the hints entry for both npm (separate import,
self-contained stylesheet) and the CDN (hints.iife.js, hints.css, and
the window.driverHints global). Theming points at the beacon CSS
variables and the Styling Hints examples. The landing marquee names
tours, highlights and hints, and the meta description mentions hints.