Update README (FragmentStatePagerAdapter)

Author: Daniel Novak

README.md

@@ -90,6 +90,14 @@ Data binding is supported - extend [ViewModelBaseBindingFragment.java](library/s
 
 That's it. You can then directly use ObservableField in your ViewModels. See [example](sample/src/main/java/eu/inloop/viewmodel/sample/viewmodel/SampleBindingViewModel.java). 
 
+Special handling for FragmentStatePagerAdapter
+--------
+The Android implementation of [FragmentStatePagerAdapter](https://developer.android.com/reference/android/support/v4/app/FragmentStatePagerAdapter.html) is removing Fragments and storing their state. This is in contrast with [FragmentPagerAdapter](https://developer.android.com/reference/android/support/v4/app/FragmentPagerAdapter.html) where the Fragments are just detached but not removed.
+We should be also removing ViewModels and storing their state to be consistent with this behaviour.
+
+<b>Use [ViewModelStatePagerAdapter](library/src/main/java/eu/inloop/viewmodel/support/ViewModelStatePagerAdapter.java) instead of the default FragmentStatePagerAdapter</b>. This class is only overriding the ```destroyItem()``` method and making sure that ViewModel is removed. The state is stored/restored automatically.
+You can also use the stnadard FragmentStatePagerAdapter - in that case ViewModels will be kept in memory and removed only when you leave the screen (Activity finished or Fragment removed).
+
 How does it work?
 --------