Doc: Edited example documentation.

-added information about how to run the example by including a file
 from qtbase/doc/global
-edited summary sections
-added \brief.
-removed image captions. Our Qt 5 CSS files don't handle them.

Task-number: QTBUG-33597
Change-Id: If3293aa9d98b662f20af2af7030b0ab0fb1e8401
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>