[bug#47343] guix-cookbook : (Basic setup with mafinests)

[Fulbert]

Hello,

I propose those changes to (Basic setup with mafinests) as they
are more likely to produce the exptected result. Probably the
`combined` search-paths profiles were not available at the time of
writing this section ?!

Although It works well for me, I'm not 100% sure it should make it
to live guix-cookbook. Not sure either if filtering-out
$HOME/.config/guix/current is necessary.

Anyway, I thought it was worth proposing :)

Best regards,
Fulbert