website: add pkg-config to Ubuntu dependencies

Corresponds to: https://gem5-review.googlesource.com/c/public/gem5/+/34777

Change-Id: I8396e4cc9210ff95e7f12e2aa57151bb3b213e49
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/34935
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
1 file changed