[documentation update] Add top level structure to new docs site

[chrisk-7777]

Core conversation here: #1033

The new document site is currently with the following top level categories: "Introduction, Recipes, etc"
This issue is to introduce a similar structure is Jotai, which is quite clear to a newcomer.

The structure will be (and can be iterated on in the future):

- Getting Started
- Basics
    - Concepts: Some of the content from first section of readme.md
    - Comparison: Similar to Jotai, and some content from the Zustand introduction section
    - Examples: Similar to Jotai "Showcase". Personally I prefer "example", to me, "showcase" sounds like production sites using Zustand. Thoughts?
- Guides
    - Updating nested state object values (from current Zustand docs)
    - Immutable state and merging (from current Zustand docs)
    - Recommended practices (from current Zustand docs - "Flux inspired practice")
    - Auto Generating Selectors (from current Zustand docs)
    - Practice with no store actions (from current Zustand docs)
    - TypeScript (from current Zustand docs)
    - Testing (from current Zustand docs)
- Recipes
    - Split recipes into individual guides (so approx 10 pages here)
- Integrations (I don't know if this is broad enough for the below, let me know)
    - 3rd party libraries (from current Zustand docs)
    - Persist middleware (from current Zustand docs)
    - Devtools (from current Zustand readme.md)
- Previous versions
    - V3 reateContext from zustand/context (from current Zustand docs)
- Migrations
    - V4 migrations (from current Zustand docs)

This can be done in parallel to the work @dbritto-dev is working on in #1008