Add a tooltip to explain what marking a preset as "runnable" does

(cherry picked from commit bc8236bd399fef0f83d4463bfd89d55004cf7a13)

editor/project_export.cpp

@@ -1113,6 +1113,7 @@ ProjectExportDialog::ProjectExportDialog() {
 	name->connect("text_changed", this, "_name_changed");
 	runnable = memnew(CheckButton);
 	runnable->set_text(TTR("Runnable"));
+	runnable->set_tooltip(TTR("If checked, the preset will be available for use in one-click deploy.\nOnly one preset per platform may be marked as runnable."));
 	runnable->connect("pressed", this, "_runnable_pressed");
 	settings_vb->add_child(runnable);