kconfig: qconf: update the intro message to match to the current code

I do not think "Although there is no cross reference yet ..." is valid
any longer.

The cross reference is supported via hyperlinks enabled by the
"show Debug Info" option.

Update the message.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>