Review UI docs: Say that files > 4000 lines are not fully rendered

Files larger than 4000 lines are considered as huge
(see SideBySide2.FileSize.HUGE) and cannot be fully rendered.

Change-Id: I7116fe16771ff43b575babbfb444a6c206650f66
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/Documentation/user-review-ui.txt b/Documentation/user-review-ui.txt
index bc476ae..aeeb842 100644
--- a/Documentation/user-review-ui.txt
+++ b/Documentation/user-review-ui.txt
@@ -1052,6 +1052,8 @@
 DOM tree, which makes the rendering slow for large files. The advantage
 of this setting is that `Ctrl+F` can be used to search in the complete
 file.
++
+Large files that exceed 4000 lines will not be fully rendered.
 
 [[keyboard-shortcuts]]
 == Keyboard Shortcuts