Outdated native setup documentation in README.md

[MichaelDark]

It is needed to update manual native integration documentation (especially for reattribution via deep links) to default recommended languages:

• Swift (IOS)
  • currently: ObjectiveC
• Kotlin (Android)
  • currently: Java

[uerceg]

Hey @MichaelDark,

Thank you for the issue / PR and sorry for the delay in replying.

In the meantime, we have migrated our docs to the new platform and in there you should be able to find Kotlin and Swift snippets.

Cheers.