Fix "Introduction" link of README.md (#3791)

Author: sekiya9311

README.md

@@ -241,7 +241,7 @@ Redux co-maintainer [Mark Erikson](https://twitter.com/acemarke) has put togethe
 
 ## Documentation
 
-- [Introduction](http://redux.js.org/introduction)
+- [Introduction](http://redux.js.org/introduction/getting-started)
 - [Basics](http://redux.js.org/basics/basic-tutorial)
 - [Advanced](http://redux.js.org/advanced/advanced-tutorial)
 - [Recipes](http://redux.js.org/recipes/recipe-index)