[DOC] New docs layout

Are are working towards streamlining the docs so that each different user persona can find what they need quickly. The current docs layout is non-trivial to navigate, and doesn't draw a distinction between content an enterprise user might be looking for vs. a database developer or standalone library developer.

Ultimately, we aim provide a few different top-level sections along with a descriptive paragraph in the front page that informs the user which sections are geared to them:

1. Getting started - a quick-start for developers and direct users. It links to the build materials and code examples to get up and running quickly. This will also link to
2. User guide - This is a compehensive guide with info relevant to all potential users (whether direct users of cuvs or indirect through a cuvs-powered integration). This guide provides a background on vector search, vector databases,
3. Develooper guide - this is for developers of both the library itself and for users integrating cuvs into a library or database.
4. Field guide - This is intended to be for end-users who might be using a cuvs-powered database- where are the install guides for various databases? what are the abi stability guarantees?

Field guide will likely be smaller than the other docs.