Update IntegrationWithExistingApps.md

docs/IntegrationWithExistingApps.md

@@ -157,9 +157,11 @@ Go to the root directory for your project and create a new `package.json` file w
 Next, you will install the `react` and `react-native` packages. Open a terminal or command prompt, then navigate to the root directory for your project and type the following commands:
 
 ```
-$ npm install --save react react-native
+$ npm install --save react@16.0.0-beta.5 react-native
 ```
 
+> Make sure you use the same React version as specified in the [React Native `package.json` file](https://github.com/facebook/react-native/blob/0.49-stable/package.json). This will only be necessary as long as React Native depends on a pre-release version of React.
+
 This will create a new `/node_modules` folder in your project's root directory. This folder stores all the JavaScript dependencies required to build your project.
 
 <block class="objc swift" />