Document Third-Party Code changes in Qt 5.13.1

The changes where obtained by running

  qtattributionsscanner -output-format json

in the sources of both Qt 5.13.0 and Qt 5.13.1 checkouts, and diff'ing
these.

Task-number: QTBUG-76452
Change-Id: Ib2dbfd8b44e440123d332d105da4dfa704ff050e
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

doc/src/legal/licensechanges.qdoc

@@ -34,6 +34,17 @@
     Changes in Qt and \l{Licenses Used in Qt}{Third Party Modules}
     released with Qt that are relevant to licensing.
 
+    \section1 Qt 5.13.1
+
+    \section2 Qt Core Module
+
+    \l{Unicode Common Locale Data Repository (CLDR)} got updated to
+            upstream version v35.1
+
+    \section2 Qt Image Formats
+
+    \l{WebP (libwebp)} got updated to upstream version 1.0.3.
+
     \section1 Qt 5.13.0
 
     \section2 Qt Core Module