docs(README): link to the docs site next to the badges (#36)

* docs: marketing-grade home + Quickstart polish

Home (introduction.mdx):
- New hero: 'Build LLM agents in Rust without the duct tape.' Three lines
  of pitch with concrete numbers (six providers, six vector stores, one
  umbrella crate) instead of a 47-word run-on.
- Shields.io badges row across the top: GitHub stars, crates.io version,
  docs.rs, Rust 1.75+, MIT, CI status. Same set the README ships, just
  surfaced where first-time visitors land.
- New 'Real apps you can ship today' strip with three Pattern cards
  (research assistant, code Q&A over a repo, streaming UI). Patterns
  was buried in 'Where to next'; now it's the second thing visitors
  scroll to.
- 'What you can build' cards re-tightened. Stateful graphs in
  particular went from a 7-feature run-on to a value-led one-liner.
- 'How Cognis is organized' (workspace map) removed from the home —
  it's internal architecture and lives in /reference/api/cognis.
- New 'What's not here yet' section, honest about LangSmith / OTel
  gaps, missing managed runtime, the smaller provider matrix. Builds
  trust faster than 'we have everything.'
- New 'Like what you see? Star the repo.' card at the bottom — explicit
  CTA where visitors finish reading.

Quickstart:
- Description: 'Build a tool-calling agent in five minutes' →
  'From zero to a running agent in five minutes.' (also updates the
  Quickstart card on the home.)
- New 'What you just built' section between the run command and
  'How it works'. Closes the loop — visitor finishes the tutorial
  feeling they understood it, not just typed it.

* docs(README): link to the docs site next to the badges

- New Docs badge in the badge row (top of README), styled with the
  project orange so it stands out among the standard shields.
- Quick-nav line directly under the badges with five jump links
  (Website, Quickstart, Patterns, API reference, Contribute) so a
  GitHub visitor sees where to go without scrolling.
- Replaced the bare 'API docs: docs.rs/cognis, per-crate.' line near
  the bottom with a two-bullet block that surfaces both the docs site
  and rustdoc.

Author: 0xvasanth

README.md

@@ -4,12 +4,15 @@
 
 **Build LLM apps in Rust. Fast, type-safe, composable.**
 
+[![Docs](https://img.shields.io/badge/docs-cognis.vasanth.xyz-D97706?logo=mdbook&logoColor=white)](https://cognis.vasanth.xyz)
 [![crates.io](https://img.shields.io/crates/v/cognis.svg)](https://crates.io/crates/cognis)
 [![docs.rs](https://docs.rs/cognis/badge.svg)](https://docs.rs/cognis)
 [![CI](https://img.shields.io/github/actions/workflow/status/0xvasanth/cognis/ci.yml?branch=main)](https://github.com/0xvasanth/cognis/actions)
 [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)
 [![Rust](https://img.shields.io/badge/rust-1.70%2B-orange.svg)](https://www.rust-lang.org)
 
+[**Website**](https://cognis.vasanth.xyz) · [Quickstart](https://cognis.vasanth.xyz/get-started/quickstart) · [Patterns](https://cognis.vasanth.xyz/patterns/research-assistant) · [API reference](https://cognis.vasanth.xyz/reference/api/cognis) · [Contribute](https://cognis.vasanth.xyz/contribute/ways-to-contribute)
+
 </div>
 
 ---
@@ -307,7 +310,9 @@ cargo clippy --workspace --all-targets -- -D warnings
 ```
 
 ## Documentation
-- API docs: [docs.rs/cognis](https://docs.rs/cognis), per-crate.
+
+- **Guides + Patterns + Examples + Reference**: [cognis.vasanth.xyz](https://cognis.vasanth.xyz)
+- **API docs**: [docs.rs/cognis](https://docs.rs/cognis), per-crate
 
 ## Contributing