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/filesystemwatcher.cpp

@@ -52,7 +52,8 @@ static inline quint64 getFileLimit()
 
 /*!
     \class Utils::FileSystemWatcher
-    \brief File watcher that internally uses a centralized QFileSystemWatcher
+    \brief The FileSystemWatcher class is a file watcher that internally uses
+           a centralized QFileSystemWatcher
            and enforces limits on Mac OS.
 
     \section1 Design Considerations