add yarn code example

Example 1: yarn add specific version

// for specific versions

yarn add [email protected]

Example 2: yarn react install

There are two ways where you can initiate a REACT app.. 
1. Using npm : npm init react-app <app_name>
	 example : npm init react-app sampleApp
2. Using yarn : yarn create react-app <app_name>
	 example : yarn create react-app sampleApp

Example 3: yarn add --save-exact

yarn add <package...> [--exact/-E]