Update validation.rst

Insert 'are' after 'that' on line 1053

Author: eightrix

user_guide_src/source/libraries/validation.rst

@@ -1050,7 +1050,7 @@ Rules for File Uploads
 When you validate uploaded files, you must use the rules specifically created for
 file validation.
 
-.. important:: Only rules that listed in the table below can be used to validate
+.. important:: Only rules that are listed in the table below can be used to validate
     files. Therefore, adding any general rules, like ``permit_empty``, to file
     validation rules array or string, the file validation will not work correctly.