Update README.md

Author: lidangzzz

README.md

@@ -4,20 +4,37 @@
 
 ---
 
-## How to read this book?
+## 1. How to read this book?
 
 This book is officially deployed at [https://hedgehog-book.github.io](https://hedgehog-book.github.io) with interactive examples.
 
-## How to build this book locally?
+## 2. How to build this book locally?
 
 1. Clone this repository to your local hard drive:
 
 ```
 git clone https://github.com/Hedgehog-Computing/docs.git
 ```
 
-2. Install next.js and its dependencies:
+2. Install next.js and its dependencies via `yarn install`:
 
 ```
+yarn install
+```
+
+3. Serve a local next.js server:
+
+```
+yarn next
+```
+
+4. If you want to build the book as a static HTML website locally, run `yarn next build` and `yarn next export`:
+
+```
+yarn next build
+yarn next export
+```
+
+## 3. How to contribute to this book?
 
-```
+s