Enable mkdocs search in documentation

Signed-off-by: Larvan2 <[email protected]>

mkdocs.yml

@@ -143,6 +143,7 @@ extra:
       link: https://github.com/SagerNet/sing-box
   generator: false
 plugins:
+  - search
   - i18n:
       default_language: en
       languages:
@@ -187,4 +188,4 @@ plugins:
           Known Issues: 已知问题
           Examples: 示例
           Linux Server Installation: Linux 服务器安装
-          DNS Hijack: DNS 劫持
+          DNS Hijack: DNS 劫持