docs(deploying): add optional cname arg in gh-page script

Co-authored-by: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>

docs/guide/deploying.md

@@ -100,6 +100,7 @@ Don't enable options like _Auto Minify_ for HTML code. It will remove comments f
            with:
              github_token: ${{ secrets.GITHUB_TOKEN }}
              publish_dir: docs/.vitepress/dist
+             # cname: example.com # if wanna deploy to custom domain
    ```
 
    ::: tip