add tooltip to send utxos button with directions on how to select multiple utxos

src/main/java/com/sparrowwallet/sparrow/wallet/UtxosController.java

@@ -16,6 +16,7 @@ import javafx.event.ActionEvent;
 import javafx.fxml.FXML;
 import javafx.fxml.Initializable;
 import javafx.scene.control.Button;
+import javafx.scene.control.Tooltip;
 
 import java.net.URL;
 import java.util.List;
@@ -44,6 +45,7 @@ public class UtxosController extends WalletFormController implements Initializab
         utxosTable.initialize(getWalletForm().getWalletUtxosEntry());
         utxosChart.initialize(getWalletForm().getWalletUtxosEntry());
         sendSelected.setDisable(true);
+        sendSelected.setTooltip(new Tooltip("Send selected UTXOs. Use " + (org.controlsfx.tools.Platform.getCurrent() == org.controlsfx.tools.Platform.OSX ? "Cmd" : "Ctrl") + "+click to select multiple." ));
 
         utxosTable.getSelectionModel().getSelectedIndices().addListener((ListChangeListener<Integer>) c -> {
             List<Entry> selectedEntries = utxosTable.getSelectionModel().getSelectedCells().stream().map(tp -> tp.getTreeItem().getValue()).collect(Collectors.toList());