website: Add new ubuntu-18.04 arm64 disk image

This is adding the new ubuntu-18.04 arm64 disk image reference to
guest_binaries page

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: I7ca78f930f597a64ccab75e09f3e5f93b101b201
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/37118
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
(cherry picked from commit e68fedaad1946e23638b5e2030e552942a1f6b78)
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/37677
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/_pages/documentation/general_docs/fullsystem/guest_binaries.md b/_pages/documentation/general_docs/fullsystem/guest_binaries.md
index 38a9f8b..8e35f0e 100644
--- a/_pages/documentation/general_docs/fullsystem/guest_binaries.md
+++ b/_pages/documentation/general_docs/fullsystem/guest_binaries.md
@@ -29,6 +29,7 @@
 
 ##### Latest Linux Disk Images (**recommended**)
 
+* <http://dist.gem5.org/dist/current/arm/disks/ubuntu-18.04-arm64-docker.img.bz2>
 * <http://dist.gem5.org/dist/current/arm/disks/aarch64-ubuntu-trusty-headless.img.bz2>
 * <http://dist.gem5.org/dist/current/arm/disks/aarch32-ubuntu-natty-headless.img.bz2>
 * <http://dist.gem5.org/dist/current/arm/disks/linaro-minimal-aarch64.img.bz2>