Doc: Added brief statement for examples overview page

Task-number: QTBUG-50261
Change-Id: Ia0daf0c5c7fc0b2e54904f0b7fe6ebe1220e5c4d
Reviewed-by: Martin Smith <martin.smith@theqtcompany.com>

examples/widgets/doc/src/fridgemagnets.qdoc

@@ -28,6 +28,8 @@
 /*!
     \example draganddrop/fridgemagnets
     \title Fridge Magnets Example
+    \brief The Fridge Magnets example illustrates how to move around several types of
+    MIME-encoded data with drag and drop.
 
     The Fridge Magnets example shows how to supply more than one type
     of MIME-encoded data with a drag and drop operation.

examples/widgets/tools/codecs/doc/src/codecs.qdoc

@@ -28,6 +28,7 @@
 /*!
     \example tools/codecs
     \title Text Codecs Example
+    \brief How to import and export text using text codecs.
 
     The Text Codecs example demonstrates the principles behind importing and exporting text
     using codecs to ensure that characters are encoded properly, avoiding loss of data