Add a note on symlink behavior of QFile::exists

Change-Id: I41ede0536f1b7093a7cde3d74a5e221df413aeea
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qfile.cpp

@@ -421,6 +421,9 @@ QFile::exists() const
 /*!
     Returns true if the file specified by \a fileName exists; otherwise
     returns false.
+
+    \note If \a fileName is a symlink that points to a non-existing
+    file, false is returned.
 */
 
 bool