Update preface

Author: udzura

book.toml

@@ -1,4 +1,4 @@
 [book]
-title = "Introduction to Uzumibi"
+title = "Beginning Uzumibi"
 authors = ["Uchio Kondo"]
 language = "en"

src/SUMMARY.md

@@ -1,5 +1,4 @@
-# Summary
-
+- [Preface](./preface.md)
 - [Introduction](./ch01/index.md)
   - [What is mruby/edge](./ch01/mruby_edge.md)
   - [What is Uzumibi](./ch01/uzumibi.md)

src/preface.md

@@ -0,0 +1,13 @@
+# Preface
+
+Why not develop [Cloudflare Workers](https://workers.cloudflare.com/) services using Ruby?
+
+This web book is a hands-on guide to Uzumibi, a framework for developing edge services with Ruby. You'll learn its core features step by step as you build real projects.
+
+Uzumibi is powered by [mruby/edge](https://mrubyedge.github.io/), an implementation of mruby. The resulting artifacts are tiny — for typical use cases, they can be under 500 KiB even after compression.
+
+We hope this book opens up a new frontier for you at the intersection of Ruby and the edge.
+
+---
+
+![Uzumibi Logo](./title.png)