Doc: Added brief statement to XML examples

Task-number: QTBUG-50261
Change-Id: I0ba4bd630746612d0f1f1632e87c6fdd6aef160f
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

examples/xml/dombookmarks/doc/src/dombookmarks.qdoc

@@ -29,6 +29,7 @@
     \example dombookmarks
     \title DOM Bookmarks Example
     \ingroup xml-examples
+    \brief Provides a reader for XML Bookmark Exchange Language files
 
     The DOM Bookmarks example provides a reader for XML Bookmark Exchange Language (XBEL)
     files that uses Qt's DOM-based XML API to read and parse the files. The SAX Bookmarks

examples/xml/xmlstreamlint/doc/src/xmlstreamlint.qdoc

@@ -29,6 +29,8 @@
     \example xmlstreamlint
     \title XML Stream Lint Example
     \ingroup xml-examples
+    \brief A commandline tool reading from an input file and writing to
+    the standard output file.
 
     The XML Stream Lint example provides a simple command line utility that
     accepts a file name as its single argument and writes it to the standard