docs(upload): improve description wording

Author: araksyagevorgyan

docusaurus/docs/cms/features/media-library.md

@@ -330,8 +330,10 @@ export default {
 
 #### Security
 
+The Upload plugin validates files based on their actual MIME type rather than the declared file extension.
+Only files matching the defined security rules are uploaded; others are filtered out.
 
-Configures validation rules for uploaded files to enhance media security.
+The `security` configuration provides two options: `allowedTypes` or `deniedTypes`, which let you control which file types can or cannot be uploaded.
 
 :::note
 It's best to define either `allowedTypes` or `deniedTypes`, not both, to avoid conflicts in file validation logic.