Assign a category to Contiguous Cache Example

Pick-to: 6.6
Change-Id: I98e62adce63df7e940d96cd50dcb243366dca216
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
(cherry picked from commit f54d222d223262b07580a082f95a9f9935d5743f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/corelib/tools/doc/src/contiguouscache.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example tools/contiguouscache
     \title Contiguous Cache Example
+    \examplecategory {Data Processing & I/O}
 
     \brief The Contiguous Cache example shows how to use QContiguousCache to manage memory usage for
     very large models.  In some environments memory is limited and, even when it