docs: use array for validation rules

It is easier to read.

Author: kenjis

user_guide_src/source/installation/upgrade_file_upload/001.php

@@ -12,9 +12,13 @@ public function index()
     public function do_upload()
     {
         $this->validate([
-            'userfile' => 'uploaded[userfile]|max_size[userfile,100]'
-                           . '|mime_in[userfile,image/png,image/jpg,image/gif]'
-                           . '|ext_in[userfile,png,jpg,gif]|max_dims[userfile,1024,768]',
+            'userfile' => [
+                'uploaded[userfile]',
+                'max_size[userfile,100]',
+                'mime_in[userfile,image/png,image/jpg,image/gif]',
+                'ext_in[userfile,png,jpg,gif]',
+                'max_dims[userfile,1024,768]',
+            ],
         ]);
 
         $file = $this->request->getFile('userfile');