fix: a grammar error in readme file

README.md

@@ -15,7 +15,7 @@ A nice place to show yourself. You can add your own information in your site's `
 ![](http://ppoffice.github.io/hexo-theme-icarus/gallery/profile.png "")
 
 ### Self-hosted Insite Search Engine
-With the help of [Insight Search](https://github.com/ppoffice/hexo-theme-icarus/wiki/Search#insight-search), you can search anything inside your site without add any third-party plugin.
+With the help of [Insight Search](https://github.com/ppoffice/hexo-theme-icarus/wiki/Search#insight-search), you can search anything inside your site without any third-party plugin.
 
 ![](https://ooo.0o0.ooo/2016/04/07/57068467ad5ea.png)