Recommend npx pod-install for setup instructions

# Summary

We've been recommending devs use `npx pod-install` since it will attempt to install CocoaPods CLI if it's not available on the computer (cite [React Navigation setup guide](https://reactnavigation.org/docs/getting-started/#installing-dependencies-into-a-bare-react-native-project)). This has proved very useful for Expo users who are now migrating to the bare workflow and want to use community packages in their projects.

## Checklist

- [x] I have tested this on a device and a simulator
- [x] I added the documentation in `README.md`

README.md

@@ -61,7 +61,7 @@ Then follow the instructions for your platform to link react-native-video into y
 
 **React Native 0.60 and above**
 
-Run `pod install` in the `ios` directory. Linking is not required in React Native 0.60 and above.
+Run `npx pod-install`. Linking is not required in React Native 0.60 and above.
 
 **React Native 0.59 and below**