docs: surface npm run demo in README Quickstart

The Quickstart block lists the basic CLI entry points but did not
include the end-to-end demo command, so first-time readers had to
scroll to the Documentation list (or open docs/DEMO.md) to discover
it. Adding it next to the other npm run examples keeps the demo
discoverable at the very top of the README.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: BunsDev

README.md

@@ -12,6 +12,7 @@ npm start
 npm run coven-code -- --help
 npm run coven-code -- -x "what is 2+2?"
 echo "list markdown files" | npm run coven-code
+npm run demo                # interactive end-to-end tour (or --auto for speed-run)
 ```
 
 The package exposes `coven-code` and `coven-code-sdk` bins.