docs / Optimize homepage

## Documentation Area
Landing page (index.mdx)

### Current Documentation Link
docs.sqlitecloud.io

## Description of Changes
1. Add SDK index page
2. Add link to SDK index page
3. Add Quick start index page
4. Add link to Quickstart index page

## Rationale
Improve the experience of first time users landing on our docs

## Examples and Code Snippets
supabase docs