qt4.inc: package qtdemo's docs in a separate package

qt4.inc: package qtdemo's docs in a separate package

The documentation was 285M and doesn't fit on the NAND of many machines,
but in another had part of the documentation is needed for the
QT demos, so we split the documentation: so qt demo only RRECOMMAND
the documentation that it really needs.

Thanks to Eric Bénard for explaining me how to split it.

Signed-off-by: Denis Carikli <denis@eukrea.com>