Clarify which image architecture is run by default
Clarify which image architecture is run by default

Given the list of architectures supported by the busybox image, it's confusing to reference "the `x86_64` variant is pulled and run" when there's no platform architecture that matches that name. Instead, changing the documentation to reference `amd64` makes more sense as there is no `linux/x86_64` architecture that's supported by Docker (AFAIK), but there _is_ `linux/amd64`.
docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,docker/docker.github.io,docker/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io