Add extended DataTable docs.

Author: yajra

buttons-extended.md

@@ -0,0 +1,17 @@
+# Extended DataTable
+
+We can now extend and reuse our DataTable class inside our controller by using `before` and `response` callback.
+
+## Quick Example:
+```php
+Route::get('datatable', function(RolesDataTable $dataTable){
+   return $dataTable->before(function (Yajra\Datatables\Engines\BaseEngine $dataTable) {
+       return $dataTable->addColumn('test', 'added inside controller');
+   })->response(function (Illuminate\Support\Collection $response) {
+       $response['test'] = 'Append Data';
+
+       return $response;
+   })->render('path.to.view');
+});
+```
+

documentation.md

@@ -77,6 +77,7 @@
 	- [Configuration](/docs/{{package}}/{{version}}/buttons-config)
 	- [Quick Starter](/docs/{{package}}/{{version}}/buttons-starter)
 	- [DataTable Buttons](/docs/{{package}}/{{version}}/buttons-export)
+	- [Extended DataTable](/docs/{{package}}/{{version}}/buttons-extended)
 	- [Artisan Console](/docs/{{package}}/{{version}}/buttons-console)
 	- [Github](https://github.com/yajra/laravel-datatables-buttons)