Correct hierarchy description in xfa/fxfa/README.md

CXFA_FFPageView inherits from CXFA_ContainerLayoutItem

Change-Id: I19e9dfc997809d304cf0bea8884d52e32995a514
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/52911
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

xfa/fxfa/README.md

diff --git a/xfa/fxfa/README.md b/xfa/fxfa/README.md
index 3b5ae9f..8845474 100644
--- a/xfa/fxfa/README.md
+++ b/xfa/fxfa/README.md
@@ -3,8 +3,9 @@
 The main hierarchy in this directory are the form elements:
 
 * CXFA_LayoutItem
-    * CXFA_ContentLayoutItem
+    * CXFA_ContainerLayoutItem
         * CXFA_FFPageView
+    * CXFA_ContentLayoutItem
         * CXFA_FFWidget
             * CXFA_FFArc
             * CXFA_FFImage