Fix the router doc

Author: gaearon

packages/react-scripts/template/README.md

@@ -822,13 +822,13 @@ Create React App doesn't prescribe a specific routing solution, but [React Route
 To add it, run:
 
 ```sh
-npm install --save react-router react-router-dom
+npm install --save react-router-dom
 ```
 
 Alternatively you may use `yarn`:
 
 ```sh
-yarn add react-router react-router-dom
+yarn add react-router-dom
 ```
 
 To try it, delete all the code in `src/App.js` and replace it with any of the examples on its website. The [Basic Example](https://reacttraining.com/react-router/web/example/basic) is a good place to get started.