Missing pod install step for installation (react-navigation#1082)

* Missing `pod install` step for installation

Need to `pod install` after installing `react-native-pager-view`

* Update material-top-tab-navigator.md

Author: Miraj98

versioned_docs/version-6.x/material-top-tab-navigator.md

@@ -35,6 +35,7 @@ If you have a bare React Native project, in your project directory, run:
 ```bash npm2yarn
 npm install react-native-pager-view
 ```
+> If you are developing for IOS, You'd need to run: **pod install**
 
 ## API Definition