Broken link, suggested fix

[Linus Nordberg <linus@nordberg.se>]

Hi,

"Debian -- Autobuilder network" [0] is linking to buildd-setup.txt [1]
which is 404.

"Since BuilddSetup - Debian Wiki" [2] claims to be superseding [1] I
think it'd be correct to change the link at [0] to point there instead.

[0] https://www.debian.org/devel/buildd/
[1] https://buildd.debian.org/docs/buildd-setup.txt
[2] https://wiki.debian.org/BuilddSetup

Thanks,
Linus