add nova

nova/src/Contracts/Previewable.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Laravel\Nova\Contracts;
+
+/**
+ * @mixin \Laravel\Nova\Fields\Field
+ */
+interface Previewable
+{
+    /**
+     * Return a preview for the given field value.
+     *
+     * @param  string  $value
+     * @return mixed
+     */
+    public function previewFor($value);
+}