feat(gitalk): gitalk config add body config item

add custom issue body configuration

source/docs/third-party-services/comments.md

@@ -150,6 +150,9 @@ Gitalk is a modern comment component based on Github Issue and Preact.
       # If you want everyone visiting your site to see a uniform language, you can set a force language value
       # Available values: en | es-ES | fr | ru | zh-CN | zh-TW
       language:
+      # If you want to customize the content of the initialized Issue, please edit the body parameters. support line breaks via `|`.
+      # Sample configuration: ${document.title}` or `${location.href}
+      body:
     ```
 
 {% note warning %}