Guides for upgrading between Input SDK versions.

- `1.1.0-beta` from `1.0.0-beta` ([Java/Kotlin](https://developer.android.com/games/playgames/input-sdk-migration-2), [Unity](https://developer.android.com/games/playgames/input-sdk-migration-unity-2))
- `1.0.0-beta` from `0.0.4` ([Java/Kotlin](https://developer.android.com/games/playgames/input-sdk-migration), [Unity](https://developer.android.com/games/playgames/input-sdk-migration-unity))