Clarify in the configure's help output that when using the configuration option -loadconfig that the file should be in the qtbase directory

Clarify in the Qt 4 to Qt 5 documentation that when using the configuration option -loadconfig that the file should be in the qtbase directory otherwise it will not work.

Generally it is expected that it should be in the same location as you call configure from but in Qt 5 the top level one is a wrapper to the one in qtbase which adds extra confusion.