Merge pull request yajra#34 from jidago/patch-2

Add docs for export column.

Author: yajra

export-column.md

@@ -2,11 +2,22 @@
 
 You can export a column customised header if manually set.
 
+<a name="export-column-with-title"></a>
+## Export Columns with Custom Title
+
+```php
+protected $exportColumns = [
+    ['data' => 'name', 'title' => 'Name'],
+    ['data' => 'email', 'title' => 'Registered Email'],
+];
+```
+
 <a name="export-column"></a>
 ## Export Columns
 
 ```php
 protected $exportColumns = [
-        ['data' => 'email', 'title' => 'Registered Email'],
+    'name',
+    'email',
 ];
 ```