website: Add the gem5art ISPASS '21 preprint

Change-Id: Ib3e0f89f4c10747f3f784d1cd1b203646ccf1be7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/42663
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>
2 files changed