docs: support pre-compressed-assets

Author: curbengh

README.md

@@ -37,8 +37,9 @@ server:
   compress: false
   header: true
   serveStatic:
-    extensions:
-    - html
+  preCompressed:
+    enable: false
+    extensions: ['html', 'js', 'css']
 ```
 
 - **port**: Server port
@@ -47,6 +48,9 @@ server:
 - **compress**: Enable GZIP compression
 - **header**: Add `X-Powered-By: Hexo` header
 - **serveStatic**: Extra options passed to [serve-static](https://github.com/expressjs/serve-static#options)
+- **preCompressed**: Serve pre-compressed assets. Run `hexo generate` before enabling it.
+  - **enable**: Enable/disable preCompressed. Defaults to `false`.
+  - **extensions**: Array of pre-compressed file types to serve. Defaults to `['html', 'js', 'css']`.
 
 ## License