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/networkaccessmanager.cpp

@@ -40,7 +40,8 @@
 /*!
    \class Utils::NetworkManager
 
-   \brief Network Access Manager for use with Qt Creator.
+    \brief The NetworkManager class provides a network access manager for use
+    with \QC.
 
    Common initialization, Qt Creator User Agent