private void showNotification(String text) {
        Snackbar.make(findViewById(R.id.main), text, Snackbar.LENGTH_SHORT).show();
    }
Function that returns a {@link io.reactivex.ObservableTransformer} which will on subscribe
set a text on a button using a proper thread

@param button the button to set text on
@param textResId the text resource id
@return the transformer
sample/src/main/java/com/polidea/rxandroidble2/sample/example4_characteristic/advanced/AdvancedCharacteristicOperationExampleActivity.java