docs: add Book Build badge to README

Author: srpatcha

README.md

@@ -3,6 +3,7 @@
 [![CI](https://github.com/embeddedos-org/eDB/actions/workflows/ci.yml/badge.svg)](https://github.com/embeddedos-org/eDB/actions)
 [![Python 3.11+](https://img.shields.io/badge/python-3.11+-blue.svg)](https://www.python.org/downloads/)
 [![License: MIT](https://img.shields.io/badge/License-MIT-green.svg)](LICENSE)
+[![Book](https://github.com/embeddedos-org/eDB/actions/workflows/book-build.yml/badge.svg)](https://github.com/embeddedos-org/eDB/actions/workflows/book-build.yml)
 
 > Part of the [EmbeddedOS](https://github.com/embeddedos-org) ecosystem.