param missing.

add param to do_upload() function.
diff --git a/user_guide_src/source/libraries/file_uploading.rst b/user_guide_src/source/libraries/file_uploading.rst
index ea2fef7..6d2106b 100644
--- a/user_guide_src/source/libraries/file_uploading.rst
+++ b/user_guide_src/source/libraries/file_uploading.rst
@@ -118,7 +118,7 @@
 
 			$this->load->library('upload', $config);
 
-			if ( ! $this->upload->do_upload())
+			if ( ! $this->upload->do_upload('userfile'))
 			{
 				$error = array('error' => $this->upload->display_errors());
 
@@ -352,4 +352,4 @@
 		image_height     Image height
 		image_type       Image type (usually the file name extension without the period)
 		image_size_str   A string containing the width and height (useful to put into an image tag)
-		================ ====================================================================================================
\ No newline at end of file
+		================ ====================================================================================================