docs: add architecture diagram to README (#65)

* docs: add architecture diagram to README

Adds a visual diagram explaining how expo-air works — the five-step real-time feedback loop from prompt to live update on device. Includes the new assets/architecture.svg with dark theme matching existing brand visuals.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

* docs: add link to original tweet in README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: improve text formatting under architecture diagram

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Haiku 4.5 <noreply@anthropic.com>

Author: GuySerfaty

README.md

@@ -14,4 +14,18 @@ npx expo-air fly
 
 Boom. You can work from anywhere.
 
-[Read the docs](https://expo-air.10play.dev/)
+## How It Works
+
+<p align="center">
+  <img src="assets/architecture.svg" alt="How expo-air works" />
+</p>
+
+expo-air creates a real-time feedback loop between your phone and Claude Code.
+A floating chat widget — running in its own isolated Hermes runtime — overlays your app
+and connects via Cloudflare tunnels to a prompt server on your machine.
+
+When you send a message, Claude edits your project files directly,
+Metro picks up the changes, and HMR pushes them to your device instantly.
+The whole loop takes seconds.
+
+[See original tweet](https://x.com/SerfatyGuy/status/2021233783769338031) · [Read the docs](https://expo-air.10play.dev/)