Update README for 0.3.1 changes

[iRoachie]

0.3.1 changes the package identifier to org.devio in commit ed6df50

This PR just updates in the installation instructions in the README

[mgtitimoli]

Great @iRoachie I was about to do the same when I saw your PR.

Don't you mind to add an entry of how to use with CocoaPods?

[iRoachie]

@mgtitimoli I'm not actually sure how cocoapods works (js developer). Maybe you could do it in another PR

[mgtitimoli]

JS dev here too 🙂.

Basically the changes I'm saying can be split into two

pod 'react-native-splash-screen', path: '../node_modules/react-native-splash-screen'

1. Move the content under Manual installation > IOS to Manual installation > IOS > With XCode
2. Add a new section Manual installation > IOS > With CocoaPods and place the following within:

1. Add the plugin dependency to your Podfile:
`pod 'react-native-splash-screen', path: '../node_modules/react-native-splash-screen'`
2. Run pod install

As a side note, I recommend you to try CocoaPods, I found it cleaner than placing everything in the xcode project file.

[iRoachie]

@mgtitimoli Best to make another PR as it isn't in line with the 0.3.1 release