Add step to copy CNAME for GitHub Pages deployment

Author: bytetang

.github/workflows/gh-pages.yml

@@ -23,9 +23,12 @@ jobs:
         run: | 
             mdbook clean
             mdbook build
+            
+      - name: Copy CNAME to book directory
+        run: cp CNAME ./book/CNAME
 
       - name: Deploy to GitHub Pages
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./book 
+          publish_dir: ./book