Update installation-ios.md (#2020)

docs/docs/installation-ios.md

 1. Install `react-native-navigation` latest stable version.
 
     ```sh
-    yarn add react-native-navigation@latest
+    npm install --save react-native-navigation@alpha
     ```
 
-2. In Xcode, in Project Navigator (left pane), right-click on the `Libraries` > `Add files to [project name]`. Add `./node_modules/react-native-navigation/ios/ReactNativeNavigation.xcodeproj` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-1))
+2. In Xcode, in Project Navigator (left pane), right-click on the `Libraries` > `Add files to [project name]`. Add `./node_modules/react-native-navigation/lib/ios/ReactNativeNavigation.xcodeproj` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-1))
 
 3. In Xcode, in Project Navigator (left pane), click on your project (top) and select the `Build Phases` tab (right pane). In the `Link Binary With Libraries` section add `libReactNativeNavigation.a` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-2))
 
-4. In Xcode, in Project Navigator (left pane), click on your project (top) and select the `Build Settings` tab (right pane). In the `Header Search Paths` section add `$(SRCROOT)/../node_modules/react-native-navigation/ios`. Make sure on the right to mark this new path `recursive` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-3))
+4. In Xcode, in Project Navigator (left pane), click on your project (top) and select the `Build Settings` tab (right pane). In the `Header Search Paths` section add `$(SRCROOT)/../node_modules/react-native-navigation/lib/ios`. Make sure on the right to mark this new path `recursive` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-3))
 
 5. In Xcode, under your project files, modify `AppDelegate.m`. add: