[2.1.x] Refs #28540 -- Added FILE_UPLOAD_PERMISSIONS to deployment checklist.

Backport of ef70af77 from master

docs/howto/deployment/checklist.txt

@@ -154,6 +154,16 @@ server never attempts to interpret them. For instance, if a user uploads a
 
 Now is a good time to check your backup strategy for these files.
 
+:setting:`FILE_UPLOAD_PERMISSIONS`
+----------------------------------
+
+With the default file upload settings, files smaller than
+:setting:`FILE_UPLOAD_MAX_MEMORY_SIZE` may be stored with a different mode
+than larger files as described in :setting:`FILE_UPLOAD_PERMISSIONS`.
+
+Setting :setting:`FILE_UPLOAD_PERMISSIONS` ensures all files are uploaded with
+the same permissions.
+
 HTTPS
 =====