Add export column Docs

Author: jsarmientoOB

export-column.md

@@ -0,0 +1,12 @@
+# Export Column
+
+You can export a column customised header if manually set.
+
+<a name="blade"></a>
+## Export Column
+
+```php
+ protected $exportColumns = [
+        ['data' => 'email', 'title' => 'Registered Email],
+    ];
+```