Doc: use standard wording in \brief commands

QDoc does some magic with the \class and \namespaces
and \brief commands, so the following wording must be used:
"The xxx class yyy ..."

Change-Id: Id231f30e8464898b776888d5423523de404aae34
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/libs/utils/completingtextedit.cpp

@@ -41,7 +41,8 @@ static bool isEndOfWordChar(const QChar &c)
 
 /*! \class Utils::CompletingTextEdit
 
-  \brief A QTextEdit with auto-completion support
+  \brief The CompletingTextEdit class is a QTextEdit with auto-completion
+  support.
 
   Excerpted from Qt examples/tools/customcompleter
 */