Add readme

.github/workflows/build.yaml

@@ -46,6 +46,8 @@ jobs:
 
   # Deployment job
   deploy:
+    if: ${{ github.ref == 'refs/heads/main' }}
+
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}

README.md

@@ -0,0 +1,17 @@
+# Context-Generic Programming Patterns
+
+## [Read the book](https://patterns.contextgeneric.dev/)
+
+## Overview
+
+This repository contains the source code for the book _Context-Generic Programming Patterns_. The published version of this book is available at https://patterns.contextgeneric.dev/.
+
+## Build Instructions
+
+This book is built using [mdBook](https://rust-lang.github.io/mdBook/). Follow the [installation instructions](https://rust-lang.github.io/mdBook/guide/installation.html) to install mdBook on your machine. You can then serve a local version of the book by running:
+
+```bash
+mdbook serve
+```
+
+The output HTML files are stored at the `book/` directory. For more commands available, refer to the [official mdBook documentation]((https://rust-lang.github.io/mdBook/)).